Re: 30+ clips split screen without FCP chugging?

try this...click: Sequence/Settings/RenderControl/Resolution/25%.
you'll be able to zip thru all your keyframes...reposition pics..etc. at a fast rate but lower resolution. when done with your composite repeat above and re click Resolution/100%.
if you have already rendered parts of the project you might have to trash those render files before you try the above.
i use this technique all the time when i have have a project that is logo-soup or heavy effects.