Q6600 running hot with Zalman cooler

I recently bought a Zalman CNPS 9500-AT cooler for my Q6600. I'm not really noticing much of an improvement over the stock cooler, with idle temps in the mid-40s and load temps of around 60 degrees. Also, one core seems to run 8 or 9 degrees hotter than the others.

I have tried reseating the cooler a couple of times, using ArtiClean and AS5 each time - no difference. I also bought a lapping kit and spent several hours carefully and slowly lapping both the cooler base and CPU, but that didn't make a difference either. I'm pretty sure I'm using the right amount of AS5 (I followed the instructions on their site) and the Zalman seems to be fitted properly.

My PC is a Dell Vostro 400, so the case is small and quite cramped with relatively poor cooling. I did expect at least some improvement over the stock cooler though. The Zalman is ice cold to the touch all the time - That can't be right can it? Is there anything I can do to improve the situation? Also, do you think a Thermalright Ultima 90 would be a better bet than the Zalman, assuming it would fit?

Thanks in advance for any help!

The 9500-AT is not a very good cooler, The core of the cooler does get hot but the fin doesn't. You will likely to find that the cooler work best when CPU temperature is higher (which it really make use of the surface area of the fins, or make the case air temperature is lower)

I'm running my 9500-AT on my Q9450 and it seems to be able to passive cool it just fine.