You can tweak the ram timings yourself so I'd go for the 6950,
I see your opting for 8Gb, do you do things apart from game on the rig?
4 is plenty for gaming,
excepting triple channel intels ofc (6Gb then)
ofc it depends what gfx your stepping up from, $240 for a small step would be painful for me to consider :P
I do actually. I do a fair bit of virtualization for school. During this semester I'll be virtualizing as much as a Windows 2008 Server RC2 with 5 or 6 Win 7 Enterprise clients also virtualized and running concurrently. I could probably shoe horn all that in on 4GB, but I'd rather not try. I'd like everything to run smoothly.
I'm building the whole thing. TOTAL new Sandy Bridge build. I'm currently using a 9yr old PC with a Geforce 7600 so... Here is the build thread. http://www.tomshardware.com/forum/303162-31-1600-sandy-bridge-build-feedback-appreciated