At least its taking off 10C on load. So, its at least absorbing as much heat as as possible.
Basically the same thing happened to me, with my Zalman 7700 vs my intel stock for my P4. It shaved off 10C off the load temp, though my intel hit 60-65C, depending on room temps.
Also keep in mind that your MB may not have the same method in determining the temp readings you see on your system. There is, to my understanding, no standard. So you can get different temp readings for same the CPU on different MB's.