It is time for an UPDATE:
Mobo: Take 3 finally came in yesterday. On April 3rd. Fuck everything.
Anyway, I went to go reassemble it and I noticed that I somehow misplaced 3 (out of a possible 4) heatsink mount screws for the CPU. Best as I can tell, I must have accidentally sent them with the RMA'd mobo, and for some reason one was either left behind, or MSI returned one to me, or who the hell knows.
Bottom line is, those are, as far as I know, fan-specific (i.e., I don't think I can just reorder screws), so I took the opportunity to make the switch to a liquid cooler. I am a little nervous, because I have heard horror stories about leaks, but I am a big fan of NZXT's build quality, and their new Kraken series has gotten great reviews. We'll see how it goes. Downside is the price, plus I have to wait yet another week for the damn rig to be back up and running.