I finally got outside to try out my Pixhawk octocopter, based on the Anycopter and some Knuckle quad parts, with altitude hold and loiter mode. Works great with no tuning whatsoever other than the calibration wizard. The octocopter currently hovers at 25% throttle, so that's not ideal because I have to give it ~50% throttle to maintain altitude in altitude hold and loiter mode, but that should improve once I get bigger battery packs and a gimbal for my GoPro.