TF2, VMware and Hard Drives

One of the biggest bottlenecks in well, all computing, but in this situation virtual computing is hard drives. Everything slows to a crawl when the drives are hit bad. Here are my recommendations for maximum Windo XP vms running Steam//TF2(hl) per physical disk drive based on RPMs. This is just what I came up with to keep the desktop responsive.
Are these numbers scientific? No. Are they what I've figured out through lots of trial and error? Yes.

5400rpm : 3 (1-2 with host OS)
7200rpm : 4-5 (3-4 with host OS)
10k : 7-9 (6-7 with host OS)

This is all assuming standard sata connectors (IDE, cut 1 per, wait, do they still exist? Oh yeah, im running 3 ;)

Don't forget to count your primary game as one instance, I recommend NOT putting it on the same disk as the VMs (the pain of waiting several minuites for everything to clear up is painful)