I suggest several changes. First off, wait for Cayman, the 6950 should be coming out in 8 days with a decent availability (says Fudzilla) Also it should cost 350$ only a little more than the 6870 for almost 40% performance increase. So that's one thing, wait.
Also, Sandy Bridge is coming out soon, doing this upgrade would be a waste. And from the looks of your parts, it doesn't look like you have a small budget, about 800$. You could do an SB upgrade.
The 955 would be a better choice, the 1090T isn't worth the cost, the i5 750 beats it out in many benchs at a lower price (190$) The 955 is just enough horsepower to handle most modern games. I play BFBC2 with my system (in the sig it has 955) perfectly fine, with my GPU OC'd to 1000/1205 I play BFBC2 at the Highest settings and get practically no visible lag.
Sandy Bridge: http://www.anandtech.com/show/3871/the-sandy-bridge-preview-three-wins-in-a-row