Hey, have you got this all setup yet? I haven't been on here in a little while...just upgraded mine tonight to RC11 and it seems to be much quicker vs RC10.
I haven't installed any extra cards yet (so far just a simple 5 disk setup) so I can't say first hand it will work but the manual says it will. I agree, it's a little overkill for unraid but I'm hoping that spending a few extra bucks will keep things running worry free for a long time.
I just went to the ASUS site and I see they have a Gen3 R2.0 version of this board that is different again. Not sure which one you picked up, but I have the R2.0. Anyway, that issue I mentioned where it wouldn't automatically boot from usb on a reboot was fixed when I updated the bios to 1302 so if you have that issue, I would look there first.