No, you really don't. That's true for the single player game, but try running your CPU at 3ghz on a 64 man B2K map and then at 4.5ghz and tell me the difference isn't noticeable.
well seen this in many articles myself and as long as you not bottlenecking your video cards shouldnt be much difference tbh
http://www.techspot.com/review/458-battlefield-3-performance/page7.html