How far do I screw down on SLK-800U ?

I recommended this sink to my friend so then we installed it the other day and I have never done a screw mounted heatsink before. After I put it in, I didnt know how far I was supposed to screw it down. Should I screw til the screws stop? I didnt want to damage his barton 2500+ so I didnt screw it down the whole way, but his full load temps are higher at stock than they were with his retail heatsink and the processor at full load @ 2ghz. I am figuring that one side is screwed down a little more than the other or something like that.

Any help?

800U Install instructions

"Tighten the heat sink mounting screws in crisscross pattern until the screws reach the bottom and stop."

Thanks for the help, that didnt help with the situation, we will probably need to reapply the thermal goop.
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