I used openelec on mine for a couple of days (remember my build, that's awfully similar to yours?) while waiting for the SSD to arrive.
I had the generic build of openelec (I believe the latest beta) already installed on a flash drive that I was trying out on another htpc. I plugged it in, and it worked without any problems. My library was mysql, hosted on my unraid server and the thumbnails were on unraid as well. Through a wired gigabit connection it was very zippy. I think the only thing that wasn't perfect was the remote. Most buttons worked fine, but I think there was no button for the context menu (I am sure that is easily fixed through keymaps)
I played 720p and 1080p scene releases and hardware acceleration was flawless. SD scene releases also worked fine. I did not try any mpeg2 stuff as I don't rip dvds and I don't record live tv. I heard openelec has problems with mpeg2
I am not sure about that.
EDIT:
I did have to apply the sound fixes for openelec. Check out this wiki page:
http://wiki.openelec.tv/index.php?title=...tion#Sound
Directly under "sound" is the fix for media playback (I forget the exact numbers for that board, but "aplay" gives you a clear description of each so it is straightforward)
And click on "Menu sounds (Most systems)" for menu sounds