ASUS N56VZ issue: Crashes when playing 3D games

Hello everyone:hi2:

I've got 2 Rams (4GB each)
one is Hyundai (the stock rom) which is PC3-12800

(Part number HMT341S6CFR8C-PB)

and the other one is Corsair (part number CMSX4GX3M1A1600C9)

using CPUID CPU-Z software it shows that both of them are 800mhz max bandwidth

after updating nvidia drivers & intel VGA drivers, i've gotten crashes after few minutes in games (with AC plugged) and without AC plugged there were major FPS drops.

even updating the BIOS to 2.17 and

setting the DVMT Pre-Allocated to 512 or 64 or 128 didn't help at all.

after using the drivers for Intel HD and Nvidia from Asus site. the crashes happens after about an hour after playing.

i've checking this forum, this thread and the 16GB thread in http://forum.notebookreview.com/ , and also in Nvidia site. alot of people have this problem and i haven't seen a solution. People have spoken about maybe the defective Optimus (changing between the Intel HD and Nvidia) which could cause the FPS drops and the crashing.

my questions is: if it was only memory, then the drivers shouldn't matter. and i don't recall that at first my computer had crashes at all.

is there any solution beside replacing the corsair memory? (like limiting the memory bandwitdh). and if not. is Kingston brand should be OK? (maybe i should replace the hyundai one)

thanks in advance:hi2:
Avishay