I say get the base model - of course, I'm biased; that's what I just got, and love it, BTW.
Also, if you feel comfortable doing
very minor computer work, replace the hard drive yourself. I paid $86 shipped for a 640GB drive, PLUS I got to keep my old 250GB and put it in an external case ($5 on eBay).
As for 5400rpm vs. 7200rpm, all I can say is
check the benchmarks. You'll be surprised to find that many 5400rpm 2.5" drives (particularly large ones) are faster than their 7200rpm counterparts. I was between a 7200rpm 500GB and this 5400rpm 640GB until I saw that the 640GB was actually faster. And cheaper, BTW.