For 4.4 - 4.5 Ghz, spend $30 on the Hyper 212
For 4.6 - 4.7 Ghz, spend $50 on the Hyper 612 or Scythe Mugen 3
For 4.8 - 5.0 Ghz, spend $80 on the Thermalright Silver Arrow
Comparison of newer coolers Corsair H series, V6GT, Silver Arrow, Hyper 612 etc....
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=797&Itemid=62&limit=1&limitstart=4
Comparison of older coolers (Prolimatech Megahalems, Thermalright Ultra-120 eXtreme, Noctua NH-D14, etc)
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=447&Itemid=62
Note: You may wanna set up multiple BIOS boot profiles on your 2600k....here's what I did on my son's 2600k
-24/7 Boot Profile - for multithreaded and every day apps @ 4.6 Ghz HT on .... Cores vary from 62-65C with Silver Arrow and all case and CPU fan on lowest possible setting.
-Gaming Boot for Cooler temps when running demanding games @ 4.8 Ghz HT off
-Test Boot @ 5.0 Ghz which is just for testing / tweaking trying new settings