1. I haven't been able to max out the CPU. I wasn't even close with 6 1080p streams going. My network was completely maxed though, and wouldn't allow me to start a 7th stream. (Edit: I just realized I was torrenting at the time, so maybe I could do a 7th)
2. My PSU is way overkill at 650W. I idle at 55W and max at 75W.
3. 12TB worth of drives in raidZ2 leaves only 7TB available. It's not a lot of space once you really start using it. If I didn't have a bunch of leftover 2TB drives (and funds allowed), I would have gone with 4TB drives. It all depends on your needs though.
4. I'm not using the M.2. I'm using a 128GB Crucial M4. I should probably find another one to mirror the boot drive.
Can you link me to the X11SSM-H board? I can't find it on supermicros site.