I say 8/10. Better than my system (duh), but I would not buy a Western Digital drive. Their warranties are not that great, and at the moment Hitachi and Seagate have the best price/performance ratio for 7200 RPM drives. Plus, most of the WD drives I've experienced have been really noisy compared to my [almost] three year old Hitachi. And that's with both old and pretty much brand new drive.
EDIT: Here's a drive that's got higher capacity and performance for the price of two of those WD drives. Why the one drive? Well, most systems actually don't notice a huge real-life performance boost from RAID. You're much better off going with a single fast drive that's big, and then partitioning it so that the OS, applications, and your pagefile are at the front of the drive, and then your documents are on a seperate partition. Also, RAID 0 doesn't always quite get along with pagefiles. And with a single drive, you'll draw less power and also be a tad cooler and quieter.