Performance Question

I've noticed that in a large (by my standards) project containing 35 tracks and 20 effects, that the performance meter is telling me that the effects are using 25% of the cpu and the total cpu usage is around 60%. Seems like a huge spread and am wondering if I got my set up wrong. What else can account for the other 35% and what does RT cpu usage refer to.

Do you have any plugins open with fancy (or not fancy but badly coded :) ) GUIs showing? Any CPU spent on plugin GUIs will not show up in the per-track plugin CPU.

I don't think so, does this spread seem high to you. Also with all plugins disabled the cpu meter is reading 25 to 30%.