7,200 to 10,000 to 15,000 RPM

What're the major differences between these three RPMs? And is it worth spending $115 on a 36.7 gb HD?
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Or is it worth paying $100 more for a 36.7gb 15,000 RPM?
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Both RPMs sound tempting, and it certainly seems like most people are wanting to switch to these HDs...

Don't forget if you get that expensive ass SCSI drive, you're going to need an Ultra320 controller to make full use of it. A quick look on Newegg shows a card that is around $120 or something but is PCI-X, something that standard desktop motherboards do not have at all.

It'd be like buying a $500 video card when all you can do is browse the web. Performance is there but you aren't/can't make the most of it.