For most things, the difference between 5200rpm and 7200rpm is negligiable... there are plenty of benchmarks (use Google) but they don't really give any indication of real life performance. Things like boot up time and app launching is sometimes noticeably different, but not nearly as much as the marketing men will try and tell you.
If you're using you Mac as a 32 track recording studio, which would require somthing like 3.2 gigs of bandwidth per minute, you'll want a fast drive - but then again if you did this, you'd probably be using a 500GB external drive anyway.
My advice is get the 100GB internal 7200 and if you're doing anything that needs more bandwidth and/or space, get an external drive. I quite honestly think that storing more than 100GBs of data on a laptop is risky anyway, it's unlikely you'll ever need that much data on the move, unless you're a HD video editor.