Your settings should be fine. Quality? 100% (it looks like you have your output monitor set up correctly - so 100% will mean that MixEmergency processes your video at 640x480 for your screen) Cache? I would just leave it on the default. If you want to lower MixEmergency's memory use, you could set it at around 400MB. Transitions to avoid? None - they're all pretty efficient. Other suggestions? Not really. The most intensive effects are the Blur based effects. On the higher blur settings they can cause problems on older models of the Mac laptops - but mostly you should be fine.
