Tom,

I lowered the whole prometeia evaporator to actually have good contact with the P4 die but I just couldnt make it work.
The best way I ever got working was with a nice shiny (silver) coldplate between the evaporator and core. Its much better contact than the original heatspreader and it got me about 60 MHz more at lower voltage. I have to say, 14 times out of 15 the contact still sucked :\
Its potentially worth it, but you'll reduce the value of your chip to practically nothing, and you will never get the heatspreader back on again. Well you can but it'll add 10-15C to your original core temp