I tested BF3 and Skyrim on my 2500k and the most of the CPU was used is 52%. That's only about half the CPU that is spread across 4 cores. 50% is 100% on only 2 cores and that was with the CPU at stock. The 52% was on BF3. Skyrim was less than 40%. On my 3960x I bet it would be less than 20% usage with these games fully maxed out.
Yeah I just read an article on Toms Hardware where he disabled the other cores then enabled etc and got an increase, everything was with max settings and a 7970 that was overclocked I believe.