I've got it running stable but had to crank the intensity and TC way down, anything above 13 and 8192 either won't launch or gives me heaps of HW errors, seems like plenty of people say 4gb of RAM is fine but a few also say you can't get over 8192 until they put 8GB of RAM, will let it run at that for now even though its only getting low 500k and try putting more RAM in it next week to see if that helps.
The tc has nothing to do with system ram. It is related to the ram on the card itself. I never could get it to work correctly in windows above 8192. In linux it is easy, the command is
export GPU_MAX_ALLOC_PERCENT=100
Somewhere I found the similar command for windows, but I could never get it to work.