I'm in the same boat. I'm pushing my dual core (E8500) to it's limits, and I decided to just bite the bullet.
My honest recommendation... is go for best for your buck, and not a "I want to play it at medium" setup because you're going to limit yourself out of the gate. Building something that just "hangs" now is going to make you in the same boat once the next engines come out and push your rig again to its limits.
I'm not saying spend 2000 on a new rig, but give yourself a little bit more wiggle room so you can push things a bit more.
With the new build, which is currently in transit, I went with a 2500K, 8GB G.Skill DDR3, and picked up another EVGA Superclocked 560 GTX (I know it's not near top of the line, but I already had one) for SLI. I'm looking forward to it, and plan to bump it to 16GB shortly as well.