Removing the heat spreader is a bad idea for one sole reason: it's almost a surefire way to break the CPU. I also want to say for LGA based sockets, the heatspreader is part of the retention design. If not that, then your heat sinks may not sufficiently press against the CPU die. And the cooling performance varies, but the question is if it's worth risking your $200+ part. If you want better performance out of the IHS, lap it (but again, this doesn't bring much performance benefit anyway)
More info:
http://www.tomshardware.com/reviews/wol ... 777-6.htmlhttp://www.legitreviews.com/article/402/1/http://www.xtremesystems.org/forums/sho ... REMOVE-IHS!