So I'm now running an i5-3570k instead of an i7-930 and the improvements are interesting.
In the past upgrades typically resulted in pretty obvious improvements, but this time, what I'm seeing is actually just as compelling but much more subtle. Basically, most of the rough spots encountered in games are smoothed out.
Take Need for Speed Hot Pursuit. On the older i7 + GTX580 I was seeing 60 fps a good 95% of the time but there were still plenty of courses and turns in which you would briefly see the framerate dip. It was nothing too severe and most people wouldn't complain but it always bothered me. Using the same video card with the 3570k, however, completely eliminates these hitches that I previous experienced. I also find that I can use 4x SGSSAA + FXAA for no penalty. It's very impressive.
Sonic Generations was another interesting one. It ran at a near flawless 60 fps previously, but I always had issues with the Chemical Plant Zone (particularly around water) where you'd see serious drops for a short period of time. Those issues are now eliminated on the new CPU.
I'm finding this to be the case across pretty much all games. Spots that used to hitch up or drop frames previously no longer do so resulting in a more consistent experience.
There are still some exceptions, though. I continue to be amazed at how poorly optimized Splinter Cell Conviction truly is. I have a fondness for the game for some reason but, man, does it run poorly. It's based on some permutation of Unreal Engine 2, I believe, and has a number of newer features implemented but it's limited to smaller levels and is only striking as a result of its art design. So, even on this setup, I STILL cannot hold 60 fps. It's close now, but there are plenty of instances where it drops well below 60. I simply cannot believe how poorly optimized the game is. Also, I cannot even use the 30 fps limit (1/2 v-sync) as that results in super lengthy loading times (which happens with a select few games including Skryim when this feature is enabled). Of course, the XBOX360 version is even more of a mess with constant slowdown, tearing, and a low resolution. The game was just very poorly coded. All of the features they bolted onto UE2 just don't operate smoothly.
Overall, though, I'm really enjoying the upgrade.