SP1 (as well as several updates) has been known to cause performance problems. Personally, many of the "tweak" sites I see have many tweaks that don't really help performance anyhow. I would do as Lord Evermore suggested, and search the forum and look at what updates have caused people trouble. I know there were several, but can't think of which (ie the recent update that disabled internet connectivity. Or the one previos that slowed some systems to a crawl) I haven't had any issues, so I don't pay these problems much atention, but I know the answers are around here if I have trouble.
\Dan