GenSeneca
@Chris21010 - Thank you for that post, it's very helpful! Are you using a hard drive you already own, or is the flash drive your actual drive? If that flash drive is your drive, you must not be using windows cuz that OS is PACKED with useless garbage that eats up space. Ubuntu? Linux? ReactOS?

if its just a folding rig and nothing else 32GB flash drive with linux installed is plenty of space. i personally like Mint as its easy to install your graphics drivers. not to mention its free ;) i also plan on creating an install guide for mint here soon.
 
as for Pcie lanes your want to have at least 8x lanes. any less and there will be a reduction in PPD. as to how much no one has really done a hard study to find out. i will also note that i did a study on pcie 2.0 x8 vs pcie 3.0 x8 and found that 2.0 was 8% lower in ppd. so if you can also try to aim for pcie 3.0, with salvaged hardware this may not be possible.

GenSeneca
Graveyard inventory:
 
CyberpowerPC (2016)
Mobo = Gigibyte GA-78LMT-USB3
RAM = 16GB DDR3 @ 2133
CPU = AMD FX-8320 @ 3.5 GHz
GPU = XFX RX 480 8GB
PSU = 600W
HDD = 2TB SATA III
 

 
 Viable choice for a single-card rig though the CPU is way overkill.
 Swap out the RX 480 for a NVidia 1070/1080/1080ti.
 If you have a lower-end AM3+ CPU with lower power consumption, it would be a good idea to swap CPUs.
 Even the Sempron 145 would be adaquate for a single-GPU setup.
 

GenSeneca
 
CyperpowerPC (2015)
Mobo = (unknown/not marked)
RAM = 8GB DDR3 @ 1333
CPU = AMD FX-4300 3.8 GHz
GPU = AMD Radeon R7 240 2 GB
PSU = 500W
HDD = 500GB SATA II
 

 
 Same recommendation as the first system, but check the PS - if it has an 8-pin PCI-E AND a 6-pin PCI-E it should have enough capability to run a 1080ti, if it only has a single 8-pin or 2x 6-pin limit yourself to a 1070 or upgrade the PS to a more-capable one (though the 500 watts in and of itself should be enough to run ANY GPU short of a Titan, how the +12VDC is set up makes a big difference).
 

GenSeneca
 
CyberpowerPC (2009)
Mobo = (unknown/not marked)
RAM = 4 GB DDR3 @ 1333
CPU = AMD Phenom II X4 955(3.2GHz)
GPU = NVIDIA GeForce 9800GT 1GB (Replaced with - Radeon HD 5870 1GB)
PSU = 700W
HDD = 500GB SATA II
 

 
 Same recommendation as the first system, unless it has 2 PCI-E 16-bit slots in which case *IF* the power supply has proper connections for 2 cards you can likely run 2 cards on this one.
 

GenSeneca
 
The remaining towers and components are all over 10 years old, so I doubt they're worth posting. Again, the towers could easily be used with new internals and the PSU's might be usable as well.
 

 
 Odds are you'd have to upgrade the PS on any such older system, but if it has a PCI-E 16-bit slot on the MB it SHOULD be perfectly able to run a single-card rig on it. I've got one of my rigs running on a old AMD socket-754 based system, with a Sempron 3000+, that pulls 620K PPD or a bit more on average with a single 1070.
 
 If it doesn't have a 64-bit CPU on it though, ignore it.
 

GenSeneca
 
So... https://pcpartpicker.com/list/CqjgxY Those are the cards and CPU cooler (I'd go to the CLC280 if needed), can you guys help me fill in the blanks for things like MOBO, CPU, PSU, RAM, so I can see what else I'd need, if I don't already have it, to build a decent F@H rig? Also, if the x8, x4 stuff is going to reduce PPD on the secondary card, it doesn't seem worth running dual cards, I'd rather just build two rigs... I have plenty of towers and PSU's to do so.

 Any I7 is SERIOUS OVERKILL for a dedicated folding rig.
 Any dual-core would be PLENTY for a 2-card rig - even the G-series dual-core Celerons would be plenty.
 Shouldn't need a high-end CPU cooler, the stock cooler is plenty as the CPU is LOAFING in a pure folding rig almost all the time (and not working REAL hard when it is pushing data out to the GPUs).
 
 8x slots on PCI-E 3.0 don't reduce PPD noticeably if at all, 8x on 2.0 seems to reduce it a LITTLE, 4x on 2.0 might inflict a 10% performance loss at most.
 16 GB of ram is WAY overkill - my 3-card rigs usually run 4GB, and I already mentioned that single-card rig that only has 1GB on it.
 
 EVGA G2 750 should be enough for a pair of GTX 1080Ti, if you want to be "very safe" run an 850.
 1000 would be right for a 3-card 1080ti rig.
 
 
 Most of my 3-card rigs are more or less as follows:
 
 AMD A10-7860K
 (I run Moo Wrapper on the APU, so this isn't a "pure folding rig" - I'd drop this to the bottom-end quad core A4/6/8 on a pure folding rig, or possibly the lowest FX-series FM2+ quad core CPUs I can find)
 
ASRock FM2-A88X Extreme 6+
 
 4 GB of whatever GSKill or Crucial DDR3 1866 is cheapest at the time.
(You could get away with cheaper lower-performance RAM but I figure someday these machines will get sold as gaming machines when I hit a "power limits, time to upgrade all my hardware" phase again)
 
 500 GB hard drive
(or whatever the lowest-cost HGST I can find is at the time, though I often go with their 3GB instead for BURST mining on - I switched from WD a couple years back after seeing the Backblaze pages detailing drive reliability and noting that WD was noticeably worse than HGST, though not nearly as bad as Seagate).
 
 2 x 1070
(some are EVGA SC models, some are Gigabyte high-overclock but NOT the G1 models, whichever were less $ at the time - my NEWEST rig is going 2 x 1080 instead)
 
 1 x Gigabyte "ITX" model short 1070
 (this card lets the card in the middle slot BREATH and stay cool - the MSI version would also work, or any other "short" card - dunno why EVGA doesn't have a short 1070).
 
 Seasonic X-850 or EVGA G2 850 power supply
(a bit overkill, I COULD get away with the 750 models based on actual measured power usage with 3 x 1070 and have some headroom but my mining area gets HOT so I prefer a bit of overkill).
 
 If I were to use a case (most of my rigs are no-case open rigs), I would use the Thermaltake Versa V35 (the V35 works the same if you prefer controls on top of the case), and remove the bottom HD cage to fit a Delta 120mmx38 (AFB1212GHE by preference) or the 140mmx38 equivilent fan in the case for proper airflow to keep the GPUs cool.
 VERY nice case, works with up to 4x dual-width cards in one machine but I'd hate to try to keep them cool packed in that tight, and inexpen$ive.
 
 If I went to 2 x 1080 Ti, I'd *probably* upgrade the PS to the X-1050 or G2 1000 model, and DEFINITELY use the 140mm top-end AFB delta fan.
 The 850 models would handle a pair of 1080 Ti and a 1070 on a pure mining rig with a low-power quad-code CPU comfortably, but would be getting a bit marginal for my preferences with the high-end APU I actually use.
 
 For a pure folding rig, you *could* swap the A10 and the FM2 motherboard for the following:
 
ASRock 970X Extreme4
 whatever the bottom-end 4-core FX-series AMD CPU is, or possibly even a dual-core.
 
 I've had one of these MB running 2 x 960 and a 950 with a Athlon64 240x without issues for quite a while now, going back to before the 10xx series was released.
 Not sure if the oldish duo-core would handle 3 CURRENT GPUs on folding - worked fine on cryptocore mining or folding on those mid-range cards but most cryptocore mining isn't tossing around anywhere near as much data as Folding does nor is the GTX 960/950 nearly as demanding as more recent higher-end cards are.
 
 
 
 I strongly recommend AGAINST the new EVGA G3 (and the Seasonic "Prime") series, as both moved to a JUNK SLEEVE BEARING fan that has zero chance of long life in a 24/7 high-load environment like Folding.
 I don't understand why they made that move - both the G2 and the X-series used a dual ball-bearing fan that had VERY good longevity and was plenty quiet, and a machine that needs the kind of POWER those series provided isn't going to be all that quiet ANYWAY.
 "Quiet" is for low-power "media center" boxes that might need 200 watts AT MOST to run on.