I was thinking of taking my 6600 gt back to upgrade to a 7800 gt or something. Which one ought I go with? I've seen them anywhere from 360 to 600 bucks and with anything from 128 to 512 ram. I do want to go with at least 256. I have seen models from evga, asus, msi, bfg, xfx, countless others. I am new to nvidia, who do I use?