I never had problems with the Q811493 patch, but from what I've read the Q330909 patch fixes the problem. Though I've never seen whether or not the Q330909 patch has the fix for the vulnerability in it. I installed the Q330909 patch anyway even though I didn't get the slowdowns.

Well I actually have Norton AntiVirus 2002 installed with auto-protect enabled and still didn't see the slowdown problem.