The difference between first generation and second generation Core processors is usually around 5-10% due to a newer and slightly more efficient architecture.
An overclocked 960 @ 4.2ghz is approx equiv of an 2nd gen at around 3.8ghz. Not that big of a difference at all when you're looking at these kinds of speeds especially for gaming which depends heavily on GPU's.
I have an i7-920 @ 3.6ghz and i'm doing alright with most of my games and i'm still running a good ol gtx260 (which IS the bottleneck).
You're fine. BF3 is fairly demanding when cranked to the max @ 1080p so it is understandable you'll experience some "choppiness" when you dip into the 30-50fps range when you're usually hovering well over 60. If you want a real upgrade than look into a GTX670 or equiv AMD GPU which provides more OOmph than any cpu upgrade can give ya.
P.S. I'm keeping my i7-920 @ 3.6 for a couple more years. Maybe add a SSD and a new GPU and it'll keep me running well for another 3-4 since it's absolutely still high end processor.