Crysis fps drop in half after reboot

So, i recently upgraded to a monster rig and decided to try out crysis as the benchmark.

much to my delight, i was averaging 40-55 fps depending on intensity of the current situation in-game. i had played for roughly 3 hours before calling it for the night, and turned off the computer.

next day i fired it back up, and... 20 fps? same settings? no change in hardware/software/anything.

what the hell happened? nothing i have done has restored it to its former glory. uninstalls reinstalls driver updates notta.

the rest of my games are still running in all their glory, its just crysis that got the drop.

im open to any ideas.

rig:

visiontek ati 4870hd 512mb
intel i7 940 @ 3.09ghz
6gb corsair 1600mhz ram
7200rpm sata 1tb hd
650watt psu

Edit: forgot to say the settings i was at, 1680x1050 resolution, all settings very high, 4x aa on.

Thanks for any help.