Well I've a laptop with a 5400rpm HDD. It's running Windows 7 very well. I think it's pretty snappy. It has no bloatware , no updates and 0 customization because it's a family computer, so I don't want any breakdown, bugs glitches whatever. I still feel comfortable using it even though my own laptop has a SSD. It reboots in 70 seconds and Firefox takes a second or two to load.
A 7200rpm HDD will give you a noticeable increase in responsiveness. Screw the benchmarks, it's really faster than a 5400rpm HDD. It cost just a little more, so I don't see much reason not to buy one.
The cache also makes alot of difference. A HDD with 16mb cache will be much faster than one with 8mb. I'm not talking about benchmarks, I mean real normal computer usage.