Well from what I have seen so far very
Temps on my X1950XTX with the stock cooler were around 55-57c idle and 75+ load. Now that's not to bad, I'm not fussed about over clocking, it was just the insane noise the cooler made
After fitting the Thermalright HR-03, which was a little fiddly for me and my big hands but I got there in the end I tried running it without a fan and just the side 120mm blowhole fan on it, a 800rpm 33.5 CFM sflex. Temps were around the same as with the stock cooler, a little lower on load, around 71c.
I had an old Papst 92mm 19CFM fan lying around so I've stuck that on and now it's sat 40c idle and hit 60c load using the ATI Tool 3D test.
For £25 it's worth it just to get rid of the noise the stock cooler puts out, lower temps are nice as well Very impressed indeed.