The i7 860, because its faster and around the same price. (hence bigger bang for the buck)
However, Phenom II's do match the i7's and i5's at gaming, and if that's your only concern, you can go get something like a Athlon X4 II 620 and spend the reset on a GPU (which would be more important anyways).
Honestly, I'd say your rig right now looks pretty good, and if you wanted to upgrade, just upgrade the Video Card.