Why just 2GB modules? You can get 8GB from two sticks these days, and it'll be more stable in general (YMMV)
Newegg.com - G.SKILL Ripjaws Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model F3-10666CL9D-8GBRL
is a great set of 8GB RAM
The 6750 is a little under powered, if you can do dual 6770's at a minimum, your performance will be much better.