Tuniq Tower or Noctua NH-U12F are both pretty good air coolers and people have got some excellent results with them. Perhaps the best would be a Thermalright U120 and add your own fan but apparantly they often need lapping to make the best contact.
Rough guess would be somewhere in the region of 3.4ghz to 3.6ghz but that is based on nothing more than me liking the numbers.