My rule of thumb for 3 needle carbs is don't touch the midrange at any time and just tune em like a 2 needle carb, the mid range isn't actually a needle but rather repositions the jet so the low needle is more tunable from low to mid and when the highend transitions.
All the guys I help out at the track also run OS and Ninja's wich are 3 needle and I tune em all like a GO anyway, except one that the mid had been moved (carby strip down and cleaned) I had to bring home and reset it and then retune from scratch.

If I get a GXII I'll probably be putting a MG carb on it anyway, I'll have to wait and see what they come up with first tho. and how it performs for me.