Just to get an idea of minimum specs, I also run a full version of MC on an Atom D2700 (2.13GHz, Dual Core, 1M Cache) client. It has 4GB of RAM and a 32GB SSD running Win7 32-bit.
I watch video w/ ROSQ without issue using the integrated graphics. Music is fine over-sampled to 24/192 w/ ~50% CPU usage while displaying Milkdrop. The only issue is that I can not down-sample SACD ISO (severe stuttering; completely unplayable). If I want to listen to them, I have to push them from the server with conversion. Navigating can be a bit sluggish sometimes as well, particularly with the remote. Navigating with Gizmo works much better, especially when playing all-day DJ and changing tracks on the fly. If I get too aggressive with flipping around tracks though (say switching tracks after listening for just a few seconds a couple times in a row), I will get ~10-seconds of stutter until it catches up. Albums/Playlists, and even changing after a complete track, is not an issue.
I'll have to post my JMark score in that thread later, but if I remember correctly, it is ~950.
PS: For people looking at DLNA DMRs, Rasberry Pi, etc for extra locations around the house, I built this client with all new hardware for < $200US shipped to my door.