Overclockers Australia has decided to pit a some of the different versions of the ThermoSonic heatsinks against each other so that we can see what difference there is. Go check out their TheroSonic ThermoEngine Comparison to see what I mean. here's a snip:

"Now that we had 4 different models of the ThermoEngine, there were three things that I wanted to compare. Firstly and most obvious, was the difference in performance achieved with different fans. Secondly, to determine if there was a noticeable difference in performance between the different colours and core types. And thirdly was something that I noticed when compiling the original roundup - the 'grey thermal phase change goop' supplied with the ThermoEngine seemed to perform the same, or better than Arctic Silver, generally regarded as the premier thermal paste."