It's almost for sure the 300s are 7200s, and most likely with 8mb, which helps too.
In inexpensive drives, a new feature to look for is "native command queueing" which lets the drive take several instructions and do them in the most efficient order. We're seeing good results with those.
Of course, I my home machine I use 3 15,000rpm disks in a RAID5 config. Opening things like Outlook take about as long as getting your finger off the mouse button.
