Try ye olde take-everything-out-one-by-one and-see-what-happens trick. Uninstalling stuff in device manager as you go.
My latest build is slow and I've just noticed that I've got cards using bonkers IRQ's (31, 36, 40 & 128) and I'm wondering how the hell that happened. This could be my problem and I'm going to see if I can get eveything within the standard 15 (without sharing) to see if it helps.
Check your IRQ's too: is your embedded controller sharing resources with the add-in card ? Dissociate them and see if it helps. And, FFS, was dual channel U/W not enough for you (!).