Hmm well I personally prefer the 7200 RPM drives. I write music for local high schools and one of the programs I use (Kontakt) needs a quick hard drive. If you're just rendering and doing CAD work, etc, I'd say just go for a big 5400 rpm drive. Will there be a noticeable difference? Maybe from time to time a slight difference during regular usage. It won't be enough to really make a difference. Load times are a bit faster for games and large programs, but other than that, there isn't a PRACTICAL difference in speed. Audio programs definitely need the speed, but I can't think of many other applications that _require_ the use of a 7200 rpm drive.
I use laptops with 5400 rpm drives every day and don't have a problem with them. Just remember that benchmarks are benchmarks - they're supposed to highlight performance differences. In the real world, chances are you wont be able to distinguish a difference under normal usage.
*OR* if you have a lot of money, you could get one of the new 200 gb 7200 rpm notebook drives!
As with the memory, in some cases its also worth upgrading the hard drive on your own as well. For example, you could order the smallest, cheapest hard drive, then upgrade it yourself and save some money. You could buy a $15 enclosure for the old drive on Newegg and have an external, portable hard drive, too. Apple's markup for this upgrade is outrageous, so definitely look into this option.
If you get the MBP, I'd get a _big_ hard drive. This way, you can have both OSX and windows and have enough space without feeling cramped. You know you'd be dual booting, so you might as well prepare for it right?