6870 isn't too much of an improvement over the 5770. See the whole 6000 series numbering went up "one hundred" so the 6870 is the replacement to the 5770. The 6770 is the replacement for the 5670. In my opinion, Sell your GPU+RAM, get a 6950 and a nice 8GB kit of DDR3 1600MHz. Most kits should be CAS9 at 1.5v or so. Shouldn't cost over $100, more around $70-$80.