I still use an i5-750, and yes, its still fine most of the time. It is getting to the point where I'm considering an upgrade, but I'm likely going to hold off until Intel releases Broadwell because it doesn't feel urgent.
You should be able to get 3.2 GHz out of it with no trouble whatsoever at stock voltage. 3.6 GHz should be easy with increased voltage. I've heard of 4.0 GHz from Lynnfield i5's, but I haven't put in a lot of effort to trying to get mine there.