I have 2 WHS:

Shuttle K45
Intel Atom 330

Specs:

Shuttle K45
Intel Pentium Dual Core E5200 2.5GHz(45nm architecture)
2GB PC6400 Kingston Memory (Dual Channel)
2 x 1TB Western Digital Green HDD.
MagicJack (US

The system draws from 49-68 watts (KillAWatt P3) on daily basis.

Usage:

1- I use MagicJack as my home phone service so the jack is connected to the server.
2- FPT server
3- Web Server
4- Torrents Server
5- Backup Server
6- GhostCast Server
7- Print Server
8- Proxy Server

We tried to fry out the K45 PSU running a CPU stress test at work. The K45 was able to handle this processor's stress test for over 30 minutes and didn't die. Unfortunately I wasn't carrying my KWP3 so we couldn't measure the power consumption. One thing is for sure: It wasn't over 100Watts or the shuttle PSU would have gone bad.

I don't know if it could manage a 65nm Dual Core CPU under stress test because I haven't test it myself but I know it handles the 45nm one "good enough".

Cheers