I experienced CPU bottlenecking in Oblivion with a Q9650@4GHz. Outside Anvil, standing in the tall grass by Anvil farm was a good location to test this.
I tested both with a GTX 260 and a GTX 570. Both was in the low 30FPS at that spot. This was at 1920x1200. Most places it ran at Vsync 60FPS though. Obviously, Oblivion is an old game and a GTX 260 was really enough to run it. Then I tried both the GTX 260 and GTX 570 in a 2500K@4.5GHz system. In the same spot I got 60FPS. There where several other CPU bottlenecking locations in the game too.
Oh, and turning down the resolution made no difference.
Pretty funny when you think about it.. GTX 260 to GTX 570 made no difference, it was the CPU bottlenecking this old game. Q9650 is not older than this game, it just goes to show how poorly coded it's game engine is. And that a CPU released 5 year later was able to get much better performance in it, due to raw power.
Skyrim uses a more modified graphics engine VS Oblivion, but still I would guess anything like a Q9xxx or AMD Phenom will bottleneck this game too. Not everywhere, but in some locations.
With full ultra and 6GB+ of HD res packs loaded i get mostly 50-60FPS with a few 40FPS spots and a very few 20fps spots. So yeah definitely some CPU bottlenecking going on. I did some simple CPU OC'ing and in the same spot getting 24FPS i was able to bump it up to i think 33 or 34 FPS
-Luke