I've done a couple more gimbal test flights ... Where to start? How about I post symptom and then action.
Apparently, the gimbal's extra 185g weight really stresses my little 350-class Nova. It's now approaching it's max. payload weight, so aircraft setup has to be extra good. These new aircraft vibrations were causing gimbal vibrations as well as general quad stability issues (as FC deals with them). It seems the brass-looking metal inserts for the main body screws were not actually fully attached to upper body shell any more. While the screw originally did tighten fully (didn't spin in plastic), the inserts could slide vertically. This was preventing them from doing their job properly. Since body is also frame, this was causing major arm flexing. To repair, insert a screw part-ways and tug to test all of them. I used super-glue and re-glued all 4 main ones (on arms, closest to landing-gear). The rest were ok at this time. If you ever see one that has backed-out ... don't just pop it back in ... it must be re-glued.
While I thought it was the gimbals weight that was originally causing the quad to fly so poorly (and for the motors to sound so labored and stressed), I think this was instead the root cause. This whole "searching for better PIDs quest" might be un-necessary.
Altitude holding worse than before. Put packing tape over 80% of new barometer-hole mod. Barometer seems more normal now.
Nova FC parameters:
I got some new (just slightly tweaked) PIDs from Skywarka on RCGroups. With the extra 185g gimbal weight, these seem to work better. See bottom of AC3.1.5 upgrade post for current ones. THR_MID=670 is finally determined and tests good at this weight.
Shoved memory-foam ear-plugs into gimbals dampening balls. Installed Mobius (and holder-tray) on gimbal arm flat with two 1cm strips of Zeal (instead of nylon 1/4" screw and washer). For extra security, I've tried a small elastic band and/or a tighter nylon tie-strap. End result is more Mobius contact surface area with gimbal arm, and seems to have fixed the "gimbal buzzing".
I'm back to using my originally posted SimpleBGC parameters. Apparently, the "whole video shot" vibrations, occasional "jello", and buzzing were all minor hardware crafting problems.
Changed Primary recording mode to 1080p/30fps Narrow. Will decrease "fish-eye effect" when camera is pointed down. While the end-effect looks like a zoom, it's actually a pixel-matched 1080p recording from middle of lens. I also tried 720p/60fps/Narrow ... while it is smoother, it's not as sharp when played back on 1080p monitor. I have it setup as Secondary.
While I think the dev's algorithm is set a bit too aggressively, I had Tower's "Imminent ground Collision Warning" go off a couple of times (still getting used to this gimbaled flying turkey). I've never heard it before so I didn't even know what it was (or if it was coming from Tower or the Taranis). It just sounds like "alternating bells and alarming". I would have preferred a voice-alert (maybe something like "PULL-UP"). A red "alert bar" appears across top of screen, but it's not like this is usually a good time to be looking at tablet.