What slows it down the most?

[zibbazabba905]

I'm reworking a video, and most of it is done, but when I'm working the preview window is too slow/unresponsive to actually "preview" anything. What extra things should I look for to speed up the project? Is it unused clips, or too many effects? is there some sort of buffer I can clear out? and is there any automated way of smooshing the clips down into the least amount of tracks needed and getting rid of unused tracks?

[irriadin]

The amount of effects definitely makes it run slow. If you can get a good sense of your video by turning them off in the preview pane, that should help a lot. If not, try changing the Preview quality to "preview (half)" or even "preview (quarter)" Using the UTVideo codec over other lossless codecs (like the appropriately named lagarith) also makes things smoother, but it's probably too late to change this if you're already reworking a video.

If you're using Vegas 11, using GPU-driven plugins speeds things up A LOT.

[Nya-chan Production]

Also Shift + B loads part of the video into memory, so that might work too, if only for a short part of the video~