*Update*

A few people have tested this and confirmed that this fixes the GK104 slowdown issue.  So, set your slot(s) to client-type beta if they aren't already, and while the slots are paused delete the beta core folder listed below to force the client to get the new version.
 
*Original*
 
Over on FF there's been chatter that the new beta version of core 17, 0.0.55, has fixed the low-PPD issue on GK104.  There's one report from a user with a 670 saying that it worked for him:
 

BleederExt64 is correct. 337.50 didn't correct the low PPD but it did run smoothly and without error on the "old" core.

Only when the v.55 core17 went beta did the PPD go back to "normal".

 
If someone could test this on their own GK104, that'd be useful.  You'd need to set the slot to client-type:beta if you haven't already.  None of the beta core 17 projects have this set as the minimum version, so you'd need to manually force an update by deleting the beta core 17 folder when the slot is paused (default C:\Users\<your name>\AppData\Roaming\FAHClient\cores\www.stanford.edu\~pande\Win32\AMD64\NVIDIA\Fermi\beta\Core_17.fah) and then restarting the slot.
 
I'd test this myself but I don't have a GK104.  I have been running this version for the last 5 days or so without issue on my 780s.  

You'd need to update your drivers to something newer to see if the problem had been fixed.  326.80 was one of the last that didn't cause this issue.  I guess you might as well go for 337.50, the newest beta driver, or whatever the latest WHQL driver is.
 
If, after updating the drivers and core, you're seeing frame times on par with what you're currently getting, that's strong evidence that they have fixed the issue.  If the bug is present, you should be looking at frame times in the 9 minute range for that project, assuming a roughly 70% drop in PPD that most others have reported.

Alright - here's what I have:
660 Ti FTW
Driver version: 335.23
Window's Vista Ultimate 64-bit
 
I was about 60% through a 9101 WU, paused it, forced the core 17 update you listed above and restarted.  My current TPF is 3:57.  I'll keep an eye on it and report any changes.
 
**EDIT: Now at 76% through the WU, I'm running a 3:54 TPF - so 'technically' lower than before.  

Just tested it now, and it's good news it seems.
 
GPU: GTX 760
Clock: 1267MHz effective
Driver: 335.23
FahCore: Core 17 version 0.0.55
WU: 9406 (19, 0, 19)
TPF: ~6:00 (pretty variable)
PPD: ~72K (inline with 327 series drivers)
 
I had tried the 337.50 beta with my GTX 780Ti and it was very wonky. It caused tons of "Bad WU" and other errors. So, I'm hesitant to try again.
 

This is great news!  Finally the gamers can update their fricken drivers without having to pay huge penalties to fold.
 
Seems a 750/750 Ti fix is in-route next.  Although we wont see what they can truly produce according to VJ.

Alright - here's another update:
 
WU: 9406
TPF: 4:10 (across 33 frames)
 
I don't think I've ever had one of these, so I don't have anything to compare against - but if I keep this rate, it's putting me almost 124,000 PPD (which I haven't been anywhere close to in some time).  I'd say whatever fix they put in seems to be working.  

Testing now looking ok tonight. I thought I would add my 780 to compare.
I did get 2 P9406 and 1 P9408 on each test set. Both Rigs are i7-3970X OC to 4.3GHz GPU's are NOT OC'ed
P9406 run nice and complete before 10 Hours
PM

Version 0.0.55 Overview Page 
Status Driver 335.23 Progress Name TPF PPD WUs ETA Core Core ID Project (Run, Clone, Gen) Credit
NoFrameTimes 0% Foldit 3 x GTX 680 Slot 00 00:00:00 0.00 0.000 00:00:00 ZETA 17 P9408 (R319, C0, G0) 13000
NoFrameTimes 0% Foldit 3 x GTX 680 Slot 01 00:00:00 0.00 0.000 00:00:00 ZETA 17 P9406 (R211, C0, G0) 10500
NoFrameTimes 0% Foldit 3 x GTX 680 Slot 02 00:00:00 0.00 0.000 00:00:00 ZETA 17 P9406 (R213, C0, G0) 10500
Running 1% Foldit 3 x GTX 680 Slot 00 00:08:16 96878.00 1.742 13:38:24 ZETA 17 P9408 (R319, C0, G0) 55615.2
Running 2% Foldit 3 x GTX 680 Slot 01 00:04:37 105728.10 3.119 07:32:26 ZETA 17 P9406 (R211, C0, G0) 33896.6
Running 1% Foldit 3 x GTX 680 Slot 02 00:05:21 84624.20 2.692 08:49:39 ZETA 17 P9406 (R213, C0, G0) 31440.3
Running 4% Foldit 3 x GTX 680 Slot 00 00:08:03 100595.00 1.789 12:52:48 ZETA 17 P9408 (R319, C0, G0) 56235.4
Running 8% Foldit 3 x GTX 680 Slot 01 00:04:30 109782.00 3.200 06:54:00 ZETA 17 P9406 (R211, C0, G0) 34306.9
Running 7% Foldit 3 x GTX 680 Slot 02 00:05:00 93834.10 2.880 07:45:00 ZETA 17 P9406 (R213, C0, G0) 32581.3

*********************** Log Started 2014-04-16T04:02:34Z ***********************
04:03:56:WU00:FS00:0x17:WARNING:Console control signal 1 on PID 3248
04:07:01:WARNING:WU00:FS00:FahCore returned: BAD_WORK_UNIT (114 = 0x72)
04:08:36:WU02:FS00:0x17:WARNING:Console control signal 1 on PID 2128
04:08:36:WU01:FS01:0x17:WARNING:Console control signal 1 on PID 2624
04:08:36:WU00:FS02:0x17:WARNING:Console control signal 1 on PID 2216
04:08:42:WU02:FS00:0x17:ERROR:103: Lost client lifeline
04:09:06:WU01:FS01:0x17:ERROR:103: Lost client lifeline
04:09:36:WARNING:FS02:Killing WU00
******************************* Date: 2014-04-16 *******************************
11:51:35:WU03:FS01:0x17:ERROR:exception: Potential energy error of 70.2513, threshold of 10
11:51:35:WU03:FS01:0x17:ERROR:Reference Potential Energy: -757984 | Given Potential Energy: -758054
11:51:36:WARNING:WU03:FS01:FahCore returned: BAD_WORK_UNIT (114 = 0x72)
 
 
AM

Version 0.0.55 Overview Page 
Status Driver 335.23 Progress Name TPF PPD WUs ETA Core Core ID Project (Run, Clone, Gen) Credit
Running 4% Foldit 3 x GTX 680 Slot 00 00:08:03 100595.00 1.789 12:52:48 ZETA 17 P9408 (R319, C0, G0) 56235.4
Running 8% Foldit 3 x GTX 680 Slot 01 00:04:30 109782.00 3.200 06:54:00 ZETA 17 P9406 (R211, C0, G0) 34306.9
Running 7% Foldit 3 x GTX 680 Slot 02 00:05:00 93834.10 2.880 07:45:00 ZETA 17 P9406 (R213, C0, G0) 32581.3
Running 61% Foldit 3 x GTX 680 Slot 00 00:08:16 96775.5 1.742 05:22:24 ZETA 17 P9408 (R319, C0, G0) 55556.3
Running 4% Foldit 3 x GTX 680 Slot 01 00:08:51 87183.8 1.627 14:09:36 ZETA 17 P9408 (R420, C0, G0) 53581.7
Running 97% Foldit 3 x GTX 680 Slot 02 00:05:12 88403.4 2.769 00:15:36 ZETA 17 P9406 (R213, C0, G0) 31923.5

 
 
PM 

Version 0.0.55 Overview Page 
Status Driver 335.23 Progress Name TPF PPD WUs ETA Core Core ID Project (Run, Clone, Gen) Credit
NoFrameTimes 0% Foldit 3 x GTX 780 Slot 00 00:00:00 0.00 0.000 00:00:00 ZETA 17 P9406 (R23, C0, G9) 10500
NoFrameTimes 0% Foldit 3 x GTX 780 Slot 01 00:00:00 0.00 0.000 00:00:00 ZETA 17 P9408 (R331, C0, G0) 13000
NoFrameTimes 0% Foldit 3 x GTX 780 Slot 02 00:00:00 0.00 0.000 00:00:00 ZETA 17 P9406 (R150, C0, G7) 10500
Running 1% Foldit 3 x GTX 780 Slot 00 00:04:03 128675.70 3.556 06:40:57 ZETA 17 P9406 (R23, C0, G9) 36190
Running 1% Foldit 3 x GTX 780 Slot 01 00:06:40 134053.90 2.160 11:00:00 ZETA 17 P9408 (R331, C0, G0) 62062
Running 1% Foldit 3 x GTX 780 Slot 02 00:03:28 162216.10 4.154 05:43:12 ZETA 17 P9406 (R150, C0, G7) 39052
Running 3% Foldit 3 x GTX 780 Slot 00 00:03:53 137096.60 3.708 06:16:41 ZETA 17 P9406 (R23, C0, G9) 36971.7
Running 2% Foldit 3 x GTX 780 Slot 01 00:06:40 134005.30 2.160 10:53:20 ZETA 17 P9408 (R331, C0, G0) 62039.5
Running 4% Foldit 3 x GTX 780 Slot 02 00:03:20 172695.00 4.320 05:20:00 ZETA 17 P9406 (R150, C0, G7) 39975.7

AM

Version 0.0.55 Overview Page 
Status Driver 335.23 Progress Name TPF PPD WUs ETA Core Core ID Project (Run, Clone, Gen) Credit
Running 3% Foldit 3 x GTX 780 Slot 00 00:03:53 137096.60 3.708 06:16:41 ZETA 17 P9406 (R23, C0, G9) 36971.7
Running 2% Foldit 3 x GTX 780 Slot 01 00:06:40 134005.30 2.160 10:53:20 ZETA 17 P9408 (R331, C0, G0) 62039.5
Running 4% Foldit 3 x GTX 780 Slot 02 00:03:20 172695.00 4.320 05:20:00 ZETA 17 P9406 (R150, C0, G7) 39975.7
Running 29% Foldit 3 x GTX 780 Slot 00 00:03:24 167667.9 4.235 04:01:24 ZETA 17 P9406 (R175, C0, G2) 39588.3
Running 72% Foldit 3 x GTX 780 Slot 01 00:06:40 134037.6 2.16 03:06:40 ZETA 17 P9408 (R331, C0, G0) 62054.5
Running 40% Foldit 3 x GTX 780 Slot 02 00:03:35 154599.1 4.019 03:35:00 ZETA 17 P9406 (R208, C0, G1) 38470.8

 
AM
P9408 Run not so well on my GTX 660Ti

Version 0.0.55 Overview Page 
Status Driver 335.23 Progress Name TPF PPD WUs ETA Core Core ID Project (Run, Clone, Gen) Credit
RunningNoFrameTimes 0% Foldit GTX 660Ti Slot 00 00:00:00 0 0 00:00:00 ZETA 17 P9408 (R435, C0, G0) 13000
Running 2% Foldit GTX 660Ti Slot 00 00:10:53 64161.2 1.323 17:46:34 ZETA 17 P9408 (R435, C0, G0) 48492.2

 
PM

Summary Overview Page 
Status Driver 335.23 Progress Name TPF PPD WUs ETA Core Core ID Project (Run, Clone, Gen) Credit
RunningNoFrameTimes 0% Foldit GTX 660Ti Slot 00 00:00:00 0 0 00:00:00 ZETA 17 P9408 (R435, C0, G0) 13000
Running 2% Foldit GTX 660Ti Slot 00 00:10:53 64161.2 1.323 17:46:34 ZETA 17 P9408 (R435, C0, G0) 48492.2
Finishing 64% Foldit GTX 660Ti Slot 00 00:10:50 64469.6 1.329 06:30:00 ZETA 17 P9408 (R435, C0, G0) 48501.4

bison88
Just for reference my OC'ed GTX 780 @ 1188Mhz (FAH 24/7 w/Boost) is doing 6 min 01 sec on the 9408.  So the numbers are looking about right depending on the exact clocks w/boost factored in.

Good to know.  I'm running a 9408 right now with a TPF of 9:35 - so probably about right on my 660 Ti.  

I installed new beta drivers, deleted old core, reset gpu slot and according to the log, promptly received version 0.0.49. ??? 
No patience for this.
 
Edit: Fixed it. I'll post back when I see some results.

I have a GTX 660 folding with the older driver - I take it there would be a benefit to upgrade the driver?

680 2gb on 337.50 running the new core17 .55 3:10tpf is about 105ppd, looks good to me so far.
 

22:11:58:WU00:FS01:0x17:Version 0.0.55
22:12:02:WU02:FS01:Upload 71.31%
22:12:05:WU02:FS01:Upload complete
22:12:05:WU02:FS01:Server responded WORK_ACK (400)
22:12:05:WU02:FS01:Final credit estimate, 14093.00 points
22:12:05:WU02:FS01:Cleaning up
22:13:06:WU00:FS01:0x17:Completed 0 out of 2500000 steps (0%)
22:13:06:WU00:FS01:0x17:Temperature control disabled. Requirements: single Nvidia GPU, tmax must be < 110 and twait >= 900
22:16:18:WU00:FS01:0x17:Completed 25000 out of 2500000 steps (1%)
22:19:21:WU00:FS01:0x17:Completed 50000 out of 2500000 steps (2%)
22:22:36:WU00:FS01:0x17:Completed 75000 out of 2500000 steps (3%)

 

I updated my 780's both core and drivers today and getting about the same numbers.

Zagen30
I don't think there's much folding benefit to the newer drivers; at best, you might shave a few seconds off the TPF.  The main issue has been those who want or need newer drivers for various games, but were rightfully unhappy with the massive folding hit.

Then would you recommend going back to the older driver on rigs that are used only for Folding for GK107 cards and below?
Thanks

robbysites
On the other hand I have the GTX 780 SC also folding 24/7 using version 334.89 - Would there be any advantage (for folding) to go to a newer driver, and if so what version? Thanks.

That second or two I've been mentioning seemed to come when I upgraded to 337.50 from 335.23, and that was on a pair of 780s.
 

bcavnaugh
Then would you recommend going back to the older driver on rigs that are used only for Folding for GK107 cards and below?
Thanks

No, I wouldn't.  You'd gain nothing from that.

Based upon my numbers I would say the new update works.  Running Core 15's 762x:
GTX 590s: 7:30-7:45 tpf 24-27k ppd
GTX 770: 4:20 tpf estimating 229k ppd!