barefeats.com did some testing of the various drives: here's their conclusion,
CONCLUSIONS
These latest test results reveal that,
a) The 7200rpm drives are the fastest when empty...
b)... but if you have 74GB of data on each of the drives, the 4200rpm drive was actually faster. That's because 74GB of data puts the 7200rpm drive at 80% capacity while the 200GB 4200rpm drive is only at 40% capacity. (See "74G Mark" graphs above.)
MacBook Pro - various drives compared
If you're planning on getting the 2.0 white MB, the upgrade from 80 GB to 200 GB costs $350, the upgrade to 160 GB costs $250. Frankly, paying Apple that much for an upgraded HD is silly. It's so easy to exchange the HD yourself, and it doesn't void your Applecare. You're better off getting the stock configuration and eventually getting the best deal you can find on a larger HD along with a 2.5" SATA firewire enclosure for the stock HD. That way you'll have an external, small firewire HD for backups and everything else.