...Ehhhh, I would strongly recommend reinstalling SP2, as your computer is incredibly vulnerable now from internet attacks. AVs and firewalls won't protect ya from these.
What I think the problem is is that your computer is overheating--and hence, removing SP2 lowered the usage a tad. Instad, I would reinstall SP2 and see if this is the problem. (try running it again with a fan blowing into the inside of the case).
Thanks.