i have an acer with XP64 & 4gb DDR3 ram. i also stripped out XP and installed NO updates.
including Ableton & Sound Forge & all my plug ins, my ENTIRE OS is less than 4.5gb & it runs like a speed freak with a tail wind.
my XP64 desktop has 8bg matched DDR3 & it is brutal fast. when your not up to your eyeballs in virus crap &
as for your mac, lets hope ya dont need to put a file bigger than 4.5 gb on it.. good luck with that ;0)