Regarding GPU HSF's and TIM's vs. paste
 

Stock crappy gpu hsf's always come with TIMs, and I'm wondering if those may be best. Thermal paste is designed to work under a certain level of compression, and those little white spring clips likely do not apply enough pressure to do the job.

The better solution, employed ideally in the swiftech geforce4 gpu block, is the use of bolts with springs, just like we use for (AMD) cpu's. Granted this probably isn't very important for large core dies like the Gef4, but may be for the ATI 9x00, and will become more important in the future (with further die shrinks).

I figure the first thing anyone here does when they buy a new card is pull the HSF, scrape off the TIM, and apply some good thermal grease. I've always done it anyway.

Has anyone done temp measurements to prove that this is in fact beneficial?

temperature comparisons no. I have tried mounting aftermarket heatsinks with thermal tape though on video cards and found no difference in overclockability. Switched to paste and immediately got bigger overclocks. No reason that you can't get springs and metal screws for the GPU or NB though. Just make sure you use a spacer so you dont short anything out.