WC10 sizing guide is available, not much different than WC9, other than only 64-bit servers are supported.
I find the recommendations to be low if you expect fast response from your system.
I have doubled the number of users expected to get a decent machine.
I just had IT install 4 HP DL380 G7 X5660, 2.8Ghz, 24 cpu cores, 36GB and 2.4TB of disk space. 2 for production and 2 for development.
The key to Windchill performance is memory for the method servers, then cpu speed.
Thank you,
Ben H. Loosli
USEC, INC.