I have both lol. I also have Tuneup Utilities which has a more advanced CCleaner startup manger. Guess I should use em and my harddrive was defragged yesterday
You Memory and Processor aren't the bottleneck, it should be running better than that. Turn off a bunch of the applications that you don't need, make sure that not only all of your wow clients are running at low settings, but also maybe set the resolution down to like 800 by 600.
You should just format. Make it nice and clean.
And install XP because you only have 4gigs ram so no need for 64bit.
And XP will use a lot less resources then Windows 7.