- Longest current 3-fan (non-reference model) cards are 13"/33cm long e.g. GeForce GTX 980 Ti ArcticStorm is 12.4" long, so they're running into the space occupied by your hard/DVD drive cabling
- Look at hybrid (water block and radiator built in) like EVGA's, tho that didn't get great reviews (too much noise, not enough overclock OC)
- Get a full size motherboard (ATX) and full size case (no mini ITX or mini anything)
- Power supply needs to put out at least 700 watts and have PCI-e connectors for 2+ video cards
- Motherboard/chipset should supply 16 PCI-e 3.0 lanes for each of 2 video cards. The devBox clones use X99 motherboards. The Z170's are showing up in deep learning rigs also. In general, older Intel X-series chipsets are preferred to Z-series
- A pair of air cooled GPU cards need to have an empty slot between them to exhaust hot air
- For double precision arithmetic, the Titan Black and other Titans released prior to Titan X have 3:1 ratio of FP32/FP64 units. All of the 900 Series cards have 12:1 (I think)
- For used desktops, Sandy/Ivy Bridge I7's and X79 chipset motherboards are a great option: Sandy/ivy/Haswell/Broadwell benchmark
- newegg is a good source for component specs, they try to standardize to some extent. Also anandTech.com, phoronix.com and pcGamer.com for reviews
Benchmark, Stress/load test
- GPU-Z and Furmarks will load your card, log temp, ASIC %age, core usage %, fan speed, # PCIe lanes in, etc. Ideally you'll watch these before buying used cards
References:
Tim Dettmers blog
R. Pieters blog
This one's mistake is a motherboard that only does 2x8 PCIe lanes to 2 cards (Z97)
Karpathy's Nvidia DevBox clone:
another devBox clone
