I recently jumped from an i7 930 @ 4GHz to an i7 2600K which is churning along @ 4.8GHz (and I'm also in the same boat where I have a 1080p @ 120Hz monitor). Most of my games are little to no change but some of them the change is definitely noticeable but not enough to truly appreciate and others still it was very significant
For instance I'm a huge BC2 fan and the change helped with my minimum frame rates but not enough to truly care as worst case scenarios for my SLI GTX470s on the 4GHz 930 was something on the order of 80fps but only due to strange graphical anomalies (for whatever reason the frame rates dive when going through the caves in Vientam)
However when playing StarCraft 2 my frame rates rose almost linearly with increase in CPU speed, now my minimum frame rate hardly ever goes below 60
those are FPS games you chose to show off, CPU can affect other games far more such as StarCraft 2 where change in clock rate alone can have just about a linear effect in performance increase, so a ~4.6+GHz 2600K would smoke a 3.7GHz 930
again, it really depends on the game