The brands don't matter, it just has to be the same gpu. you can also mix the onboard ram. lets say you get a 768mb gtx460 and a 1024mb gtx460. It would just use 768mb on the 1024mb card.
I get the same BSOD NTOSKRNP.exe+70740, This only happens when I play crysis
I think its the sli patch also.
Not just you
EDIT** I figured out that if I overclock my video cards it gives me that error
you might of moved on but have you tried the latest 1.0patch from xdevs, here is the link
http://www.xdevs.com/sli/SLIPatch_v1.0_final.exe
Works with my @xgtx570 on driver 266.58,Windows 7 64bit with 790fx chipset
kk it was worth a shot. Some people were having that problem mentioned a few pages back with older cards and the slipatch. Only thing I can say is revert back to old drivers and wait for a new slipatch to come out.
Only thing I can say man is just try it out. A lot of people if you read a few pages back about flickering. It might work cause other .dll are conflicting when you install the new ones. Try it out and report back to me. Also I never had any problem like you. Mine pretty much worked the first...