I've discovered (and confirmed with SF) a huge performance tip for those of you who do heavy editing on a single track, or have large projects in general:
Use multiple tracks for your editing and this will free up resources and any slugginess in general. As soon as you find perfomance slow down, drop your material to a new track and suddenly it's like a new project.
I found this because I was editing an audiobook which can easily get to be up to 6 hrs long. After a few thousand edits, the zooming and general performance of Vegas became very slow - thus editing became slow. So I decided to create a new track and continue editing on that one and it was as though I had created a whole new project.
Hope this helps some out there...