|"The two PCI-E 2.0 16x slots run in 16x mode when doing SLI."|
Does the mboard manual state that ?
"I'm also considering water cooling the two cards, but even a basic setup from koolance would cost $500+."
Much cheaper alternatives would be
- should work -
- an aftermarket fan that yields more space between the fan and the card next to it
- an aftermarket fan / heat sink combo that yields more space between the fan and the card next to it and has a better heat sink, such as one with heat pipes.
- WILL work -
- mboards are relatively cheap - get a different mboard that has two PCI-E X16 slots farther apart, which is the usual situation, that is compatible with the same cpu and ram - you may be able to find one with the same, or a similar, superior main chipset.
Sell the mboard you have now, while it's still worth a fair amount.
You could always try one card in a X16 slot, the other in the X8 slot to see what the difference is, though you may need to run some performance tests with the present situation and compare that to the latter to give you some real data.
Why do you want to run two of these cards ? From what I have come across so far, just one has extremely good performance.