Jon (JFettig) speaks the truth. Specifically, check out the
Heatsink Roundup at overclockers.com. Joe does a good job of reviewing heatsinks without bias, and with fairly good test equipment. I've owned many aircooled heatsinks, and found that my results and his correlated nicely.
If you want absolute performance, be forewarned that the fans are going to be LOUD!!! If at all possible, try to go to a local computer shop and listen to some of these 6000-8000 RPM fans before you buy, it may change your mind and save your ears.
Good luck!