Atom vs Undervolted Athlon for Low Power File Server

[phpguru]

Hello everyone!

I am looking for some advice for a fileserver I'm planning to build. It will be running Ubuntu and will be running a torrent client in addition to the file server part.

With electricity prices the way they are in California, I'm looking to reduce the power as much as possible. This is where the problem lies. I have been reading about the Atom and the C6 state and how it fares to an undervolted Athlon since the atom runs on the 945 power hungry chipset.

Which do you think would be more suitable for this operation? The server would be idle most of the time but should be able to serve data at 60-80MB/s when called upon.

Basically, here are the requirements:
5+ SATA ports
IDE Port would be nice (for CF to IDE)
eSATA
Gigabit Ethernet
Need ability to startup at a given time

I found that the GIGABYTE GA-MA785GMT-UD2H has all of these features but still unsure if I should go with a discrete processor or Atom. I have looked into the Zotac ION but those don't have enough SATA ports to make it work for this application.

Given all this, any recommendations for CPU/MOBO? I hear the 45W new Athlons are coming out in X2/X3/X4 but I wasn't sure if I could undervolt these enough to make it worth my while.

Thank you so much!