Benches on my machine showed an almost perfect doubling of drive throughput, and timed load times of zones in WOW (using a plugin to time zone loading times) resulted in something like 25%-50% faster loads on zones, and a similar speedup in boot times on XP.
The trouble with the benches you cite is that in things like loading a zone in Quake, only a fraction of the level load time is spent loading the level off the disk, so you end up hitting Amdahl's law. They also compare a 10k drive vs a RAID array of two slower drives.
You also didn't notice what I said, which is that I have no real risk of data failure, since I have automatic backups to a third drive on my system. If I was building this from scratch, it'd be RAID5 all the way, but the marketing on the box of the mobo tricked me, and so I have an ad-hoc RAID5 with a RAID0 array backed up by a single drive.
Also, I highly not recommend buying an off the shelf Dell or whatever at your computer store. The reason they're so cheap is they cut corners where you're not looking. I can't count the number of times I've popped open a premade computer and seen a single RAM slot, or no expansion PCI slots, or only a single IDE connector, or whatever. When my fiancee wanted a new computer, I went crazy trying to find a computer that had everything we wanted (using all the build-your-own websites, like Dell's), and they either couldn't do it, didn't have it, or were grossly overpriced. So I went to Fry's and spent the afternoon building a computer for her. Not top of the line, but at that price-inflection point where things start getting cheap, RAID1 for safety, all came in under a thousand bucks. Runs like a champ.