8GB RAM is fine for gaming. If you went higher you would need to be looking at expanding the OS because Home Premium can only take 16GB and 16GB RAM plus 2GB VRAM = 18GB.
Oh and I personally would get the 7950's because of the 3GB VRAM which could be handy over 3 screens. What power supply will you be using for a multi gpu setup?
Just browsing this thread. You mentioned about the RAM limit with OS, is this the same for mobo? Just wondering because I have 16GB RAM and am looking to get 2GB DDR5 video card. If my mobo only takes 16GB (which it does) will it not work?