To answer your question, yes the Maxilla version usually has less RPM than the normal version of the Trinity series of motors (D4, D3.5, Kill Shot, etc.) because the maxilla version has a 12.5mm rotor and the standard version comes with a 12.3mm rotor. While having less RPM, the maxilla has more bottom end and most racers prefer the bigger rotor for on road. I had two Kill shot RPM motors; one with the small 12.3mm rotor and one with the 12.5mm rotor. Our large flowing outdoor track here (160Ft straight) I consistently got better lap times with the Maxilla motor even though my dyno indicated the 12.3mm rotor gave me better RPM (at the same timing).

I don't have much D4 experience, I now only have one, a 25.5 and it is not ROAR legal but it is a real screamer! I sold my 21.5D4, it was only marginally better than my kill shot (both with the 12.3mm rotor).