Quote from: GuiltySpark343 on May 05, 2013, 03:15:05 AM

I saw those from Cablesaurus ... not sure with the molex connector is for. But this could explain a lot due to differences in power specifications:

"All sizes of ×4 and ×8 PCI Express cards are allowed a maximum power consumption of 25 W. All ×1 cards are initially 10 W; full-height cards may configure themselves as 'high-power' to reach 25 W, while half-height ×1 cards are fixed at 10 W. All sizes of ×16 cards are initially 25 W; like ×1 cards, half-height cards are limited to this number while full-height cards may increase their power after configuration. They can use up to 75 W (3.3 V/3 A + 12 V/5.5 A), though the specification demands that the higher-power configuration be used for graphics cards only, while cards of other purposes are to remain at 25 W.[10][11] Optional connectors add 75 W (6-pin) and/or 150 W (8-pin) power for up to 525 W total (75 W + 3×150 W)" from http://en.wikipedia.org/wiki/PCI_Express#Power

So by plugging a x16 card into a x1 riser, you're only able to pull 10-25W max from the PCI-E side. A graphics card might be expecting 25-75W, hence the instability.

Good Find! That may well be the problem if I'm reading that right. I'm going to mod (https://bitcointalk.org/index.php?topic=76121.0) a spare 16->1x riser to have molex over the next few days (hopefully tomorrow) and will retest the system for stability and report back.

In the mean time... Anyone want to chime in on what manufacturers/vendors you like to use?