Something that was very recently brought to my attention by another engineer who's helping me archive/digitize some ancient multitrack tapes is that older Macs have a hell of a time handling long multitrack audio files, regardless of how much RAM is installed and how big/fast the drive is.
Now, "old" may be relative, I don't know of any clever way to correlate processor speed (or type) with track count & track length. And "long" is also relatve; if you're just talking about individual 4-minute tunes, there may be nothing to worry about. But when we briefly considered archiving my 40-minute ADAT tapes as 16 single contiguous WAV files, he asked me what Mac I was using and noted that his current top-of-the-line Mac Pro tower would have a hard time with files of that size. We wisely decided to chop up the files into individual takes.