I did a lot of looking around between the two. There isnt much in it, but the Thermalright Ultra Extreme is apparently the better one.
Apparently there was some problem with the bases not being flat though. But it seems to have been more with older ones.
The only thing im not too keen on is the fan clip. Would rather something more solid.
Also wish you got an extra pair of fan clips to mount a fan on the other side of the heatsink, but it wouldnt make a huge difference.
Some reviews of it showed that the Thermalright Ultra Extreme alone (without a fan) was giving better cooling than the stock intel cooler!
Also, there is a limited edition black one coming out soon.