Well...I'm running a Core i5 3570k overclocked to 4.3 GHz, and I still drop to 50 in combat sometimes. Thing is, those addons are doing a whole lot of math. You'd be surprised how much it is. In 25m raids, my addons sometimes use almost as much CPU as the client. A major offender is 'smooth updates' on health bars.
Oh, another thing that eats a shocking amount of CPU time is buff/debuff timers. Make sure your configuration isn't showing unnecessary duplicate information.
Thank you Kaels, I'll definitely do that. YEah, I finally OC'd my 965 BE but it's not enough juice. Unfortunately I'm working with AMD parts until I get the funds for a nice new mobo.