I believe we can rule out CPU being the issue. Given that both cards are causing crashes, I am inclined to believe that this is a motherboard issue (unless you are the world's unluckiest individual and both cards happen to be faulty). If Memtest comes up clean running 1 stick at a time for no less than ~8 passes, I'd contact Asus and RMA the motherboard. Since it's so new (and don't quote me on this) I am pretty sure Asus will set up and advanced RMA as long as your board qualifies for it, and they will send you a brand new one before you even have to send yours out.
Now here's the choice you can make to go a step further:
1. Asus advanced RMA sends out a brand new replacement board, and you don't have to send your old board in for ~3 weeks from what I recall. So what you can do is you can wait for the board replacement to come, see if the issues stop all together, and then send out the board. You'll be able to use your computer how you are now, but with obvious crashes here & there.
2. You setup an RMA with Asus just like you would in choice #1, however, rather than being able to use the computer with frequent crashes, you can also go a step further and contact EVGA for a possible RMA on both cards as well just in case. That way, you'll have a new replacement board and two new video cards.. so if you crash again, well... it really narrows it down quite a bit.
Regards,
Patrick
