Your budget is really going to be your limiting factor. I have an i5 4690k that I have overclocked to 4.5GHz on air (with a very large cooler). Getting 4.4 to 4.6 on this processor on air shouldn't be an issue. It can handle most things I throw at it. A few minor slow downs here and there on modern systems (PS2, GC) depending on the game, but not that many. It can be had for about $220 right now. Get that and a good cooler, and you should be pretty happy with it. Go with a liquid cooler, and you might squeeze a few more MHz out of it.
Or if budget isn't a problem, go for an i7 6700k for around $360. Those are rumored to run at 4.5 to 5.2, with most people reporting the 4.8 as average.
But as with any overclock, your mileage will vary. There are a lot of variables in it, even the CPU itself. You can get 5 of the exact same CPU, put them all in the exact same set up, and get 5 different max speeds.