Oddly enough, I ran 4GB ram on a Mac system, Cubase 6, fairly big projects, Trilian, NeoSoul keys, Halion… really did not have a lot of problems, occasional would lose power and audio would start to screech, but it held itself together pretty good, considering Cubase is not known to be efficient on MacOS, it may not be as powerful, but it can run on close to nothing.
Upgraded 64 bit, C7… only a short time so far, but on a Mac there are no such performance increases. I can not say “Oh so glad I’m 64 bit!!!” It is not like that over here, it feels a little good to be up to date, but there is no wow factor from quadrupling the memory Cubase uses. Still load up DC8C, anything with oversampling, still 50% ASIO is used, just like 4GB ram 32 bit.