Furmark is flagged inside the nvidia driver so it won't stress the GPU as much as a game will. If the 470 works without issues then that pretty much tells you the 660 has a problem.

Any idea why my 470GTX has 2 6-pin power connectors but the 660GTX has only 1 6-pin?
 
My PSU should have more than enough juice to power the 660 under load.
 

Mower
Any idea why my 470GTX has 2 6-pin power connectors but the 660GTX has only 1 6-pin?
 
My PSU should have more than enough juice to power the 660 under load.
 

is normal. 
 
u can check ur CPU temperatures too. furmark do not stress CPU only GPU. maybe ur pc reboot for that reason. 
 
if ur temps are ok u should RAM ur GTX 660. if the GTX470 work with no issues. 

Mower

SajinThe 470 uses more power than the 660.

Yep, I assume so.
 
The 660 worked fine on my brother W7/64 PC yesterday but reboots on mine under load.  So, in IYHO it could only be the card, given that my 470 still runs fine?  I ask because its outside the 3 year warranty period.  Cheers.

Reboots during gaming are usually caused by a faulty PSU, overheating hardware could also cause rebooting. Maybe your PSU is at fault, only way to test would be to buy a new PSU and put it into your rig to test or use a multimeter to check the voltages while under a load to see if they are within ATX specifications. Since the 660 worked fine in your brothers PC I would start by swapping/testing the PSU with the 660 in the system.
 
You could also try the following to see if it causing your system to reboot... Run Prime95 & Unigine Heaven 4.0 at the same time with the 470 in the system. Start Small FFT test inside Prime95 first then startup Heaven 4.0. You will notice lag but it's completely normal since you will be putting your entire system under a full load. If your system reboots while both tests are running your PSU has a problem.

No effect, I give up.
 
Thanks for the input, folks.

Good deal. How does it run at stock clocks now? 

Underclock core & memory by 105MHz together. You could try rasing the voltage if underclocking isn't working out for you. Power target is the voltage ceiling for the card, raising it allows the card to pull/add more voltage when necessary if needed.

Wouldn't underclock anymore. Go back to the 470 for now. RMA the 660 if you can to see if it helps with the issue. If the RMA'd card fails to correct the problem replace/RMA your PSU.

Still reboots.
 
Going to try this:
 
http://forums.evga.com/PR...LOGIN-FIX-m586183.aspx

Looks like it's time to do some RMA's, buy new hardware, or stick with the 470 for now. 

Mower
What voltage level would be safe to push the card to?
 
Cheers.

Anything that is allowed via afterburner/precision is safe.

Maybe a stupid question but here goes.
 
I have a Ultra x3 600W ATX PSU.  It's modular.
 
Now, for the GPU, do I need to be using a power cord that plugs into any specific power port on the PSU to get the 12 volt rail?

Roger, will check, cheers. 
 
I assume on a single PSU connector card like the 660, it doesn't matter which power port on the PSU I use...
 
I really want to salvage this card.

Got the card from my brother and there's 300 days left on the warranty, may submit a Guest RMA, if so...hey EVGA!  You can see I tried...LOL!