I had a Freezer 7 Pro rev 2 cooler and it did a decent job cooling my lower mid-range dual core processor in my P35 system.
It's not adequate for quad core processors, especially when they're overclocked.
If you want to overclock your 2500K to ~ 4.5GHz, you'll need a high end air cooling setup or a mid-priced all in one water cooling unit.
Trying to get by with an inexpensive cpu cooler is as bad as using a cheap power supply; both are bad ideas.
See what others are using with their overclocked Sandy Bridge K cpu's.
**edit** You will be better off going with an Ivy Bridge motherboard now, even if you are buying a Sandy Bridge cpu.