You might also want to look at the Cache abilities of all your Macs. Cache memory acts as a buffer between data paths and can save you time when running repetitive tasks. For more Cache information look at me page here . CPU chip - Mac games in particular are setting a trend on what processors their software will best run on. You might want to upgrade your old Macs with either NuBus or PCI G3 cards.
Many applications require quite a substantial disk presence.
Work with what you have. You can save space just by compressing. I have around 4Gb of compressed files on my iMac, not important files, but I still need them on the drive ready for reference. Look for 'bloatware', in other words control panels or extensions you don't use or need any more. Mac compression utility is Aladdin Systems, Stuffit, click here for further details .