the manual says preferred quicktime is jpeg compressed, 320×240 but that obviously looks a bit crap!
do you generally air on the side of caution? im guessing not but who wants to crash the program in the middle of playing live! well.. if anyone has experience w/larger resolution and no crashing, do tell!;)
for starters I would investigate using openGL for video processing. the syntax is a bit different and confusing at first (at least for me) but it ends up being much easier on your CPU. search the forums for vade’s jitter optimization methods (he also has a zip with some cool FX units [shaders] on his website.) also, look for the ‘jitter-examples’ folder on your hard drive to get a handle on chaining.
but generally speaking, the more fx you have chained together the worse the performance. it all depends on how much lag you’re comfortable with. for me, this has been a much bigger factor when optimizing performance patches than the actual video formats themselves
If Max is crashing, you should let support@ know. Usually the big concern with live video is maintaining framerates. Best way to do this is to make sure ALL your content is in a realtime-friendly format (photo-jpeg, ProRes 422, AIC, etc.) and to limit processing to what you will actually use. Best thing to do is to try it out and see what happens.