Olliw or Luv I got some tail twitching. I had the rate gain set at 1.70 then 1.23 and did not see much differences whats your suggestion?
I have absolutely no idea what a "twitching" tail is...
anyhow, if you are after a systematic tuning procedure set first I to zero. Then increase P step by step until the tail wags in hover. Reduce P such that the tail doesn't wag. Now increase I step by step until you are happy with the heading hold. Whenever you increase I you likely have to reduce P a bit to get rid of tail wag. Now do aggressive moves, when you observe tail wag reduce P a bit. That's it.
The default I value shouldn't be too bad, maybe its a bit too large. Since you have quite powerful motors I would think that the default P value is certainly too large.
As Luv said many other factors can come in. A rigid tail is one of them. Other parameters are also available, which hoever usally don't have to be touched. However, since you had the coaxmixer version before on the same heli, you have a good reference... with the gyromixer it should fly at least as good as that... if not, we need to do go a bit deeper into your setup