Its got 4gb of RAM and 4x 2tb drives with 3 of them in RAID1 (where the movies are) in Windows 7 Home Prem 64bit.
Did some tests this morning, nothing comprehensive just with task manager. Ill break out perf mon later I think.
Anyhow...
AirVideo - Basically depending on the content it will peg both CPU cores at 100% when transcoding which is likely the reason for the buffering etc. Ive found however it does depend on the content, as AVI's, MKV's and MP4 files all have different behaviours i.e 100%, 75% and 1% respectively. Looks like Air Video has different code paths for different content, makes sense. Surprised MP4 just streams with no transcode; I guess Ipad supports it natively. I'm going to try varying bit rates next and see if that works better, but it seems like on the fly transcode doesnt have the necessary horsepower.
SMB Streaming - Very unscientific but with just streaming a file through SMB/CIFS through to a Zotac Zbox running XBMC Live 10.0 the little box is not even breaking a sweat, and barely registering any CPU activity which is good if a little unsurprising. The glitches im getting in XBMX (buffering) will require more investigation. Im going to break out perfmon and look at the disks next, but to be honest I cant see it being that unless Windows is doing something cack with that RAID array.
FYI, Im also running tonkymedia server for MP3 serving and it works great to a streaming capable tuner/dock I have.