well id be more interested in the temperatures..........when mine are by themselves, cloaked at 900, they dont go above 60C, stable, but when in sli, the top card hits 75C, and becomes unstable. So id say you just need to keep an eye on your temps, because the warmer they get, the higher chance to become unstable.
This is why using watercooling can help achieve high overclocks because the chips stay much cooler, hence are more stable and can also hit higher clocks with lower voltage.If they are definately both 100% stable by themselves, then it must be temperature related.
Check them by themselves again, keep an eye on temps, makes SURE they are completely stable, let each card do 5 runs of unigene heaven.
then run them in sli, see if the temps are any different, again run unigene. Mine would crash around run three when in sli because the top card was now much hotter.
Only then once you discover whats causing it can you adjust, and fix the problem.
No amount of fan increased helped me since the card was being starved of air.
Edit: and you dont want the setup being too noisey, if I was you and they need a noisey fan speed id just run at 950 and be happy with a quieter system, 50mhz wont make much difference maybe 1-2fps
Hope you get it sorted
Edited by Juliancahillane - 4/4/11 at 5:16am