Are the load temps higher or lower than what they were with the other sink? From my experience, the h50 fluctuates less (maybe higher idle) but keeps load temperatures lower. The thermal compound provided on he h50 is actually quite good, and as far as the curing period goes, yes, you probably will see slight temperature drop after a couple of weeks. However, at stock settings, my 955 runs full load at 47c at 18c ambient in a less ventilated case.
One thing to check: make absolutely sure the h50 fan is pushing cold air in from the outside and not pulling hot air over the radiator.
Hope that helps!