Though I have not bought the Acto MX, I am going to for christmas. I have done a tone a research on the Acto and Gamma. I was trying to decide between the two as well. I just totally revamped my system. I use to use Synthetic jacket like the montbell thermawrap and arc atom lt and would sweat WAY too much. Now...
Base Layer: Ltw meriono wool like Rho Ltw
Midweight: Acto MX
Outershell: Just got the Alpha FL to specifically go with Acto- I have the Alpha LT as well and I am going to most likely sell it. 3 Layer Gor is way tooo much. Excited to try this piece. The two layer will hopefully be breathable enough. If not I am done with Gor.
Pants: Gamma Lt - No gaitors, using bungee cords w/ grommets
Synthetic Belay Jacket: Dually, Kappa, Patagonia DAS type of jacket
Synthetic Pants: Atom Lt
Personally I am going with the acto. I have used the gamma a couple times and like it for trips to Ouray but not for alpine climbing, mountaineering it seems like acto is going to be a game changer for me personally.
Sorry I dont have first hand experience in the field. I have tried on the acto and it is a top quality jacket. Ill let you know in a couple months how it all plays out.