oh yeah ... 20 - 25% of what?
keep in mind there is a certain *spreading* of used memory depending on the situation you're in .... watch your activity monitor which app is using how much memory (and which kind of memory)
VI/VE works up to say 3.2 GB (physical) memory used, but you might run into a situation where memory fragmentation results in problems loading huge arrangements ... it often depends what you have done before and how clean unloaded stuff leaves your memory.
hth, christian
and remember: only a CRAY can run an endless loop in just three seconds.