Crysis Warhead was not as intense as Crysis was but it can be quiet the hog. There are some tweaks you can do to make it much better and I think you can find them even here. If not Google is your friend.
I usually let the game dictate what the best or optimal settings are and I go from there.
It appears you are using the latest drivers
for your video card but, what about your sound & monitor? do they also have the latest drivers? Outdated audio drivers can run a mock as well... personal opinion of course but I do Off-Line Gaming quiet a lot.
This is all I can think off at the moment, I am sure others will chime in soon enough... hang it there... we'll get you shooting w/o hiccups yet