Sold two more of my i5s and used the proceeds from that to buy another 4P setup. Supermicro H8QGi-F setup with the [H] OC BIOS preflashed, 4 Opteron 6172 CPUs (2.1GHz 12C PhII gen), and 4 2U G32 coolers. Despite being a somewhat older board it still supports the newest Opteron 6300 series CPUs, so once the prices come down a bit I can upgrade to those.
Also--looking at getting some new G34 heatsinks for the 1U setup--if I leave the top off, I can use regular 92mm or 120mm coolers. Gonna see how the OCed 115W CPUs do with the Supermicro 2U coolers because they're cheap (~$30 each vs $60 for the Noctua ones). But either way before too long I'll be getting new heatsinks to quiet it down a bit