Are unable to max out any games to the fullest?
New CPUs are right around the corner so if you can hold off for a bit I'd do so.
The E8x00 CPUs will bottleneck GTX 470 SLI slightly, but it shouldn't be too much (assuming your resolution is 1920 or lower), and the games should still be at more than playable frames.
I'd hold out for sandybridge.
E8x00 CPUs (especially at 4ghz) are still badass gaming CPUs.
Check out this review with 5870 crossfire (near your setup) on a ton of different CPUs on both 1680x1050 and 2xx0by1xx0