The other thing to consider is that 2-strokes and 4-strokes deliver their power a little differently. A 2-stroke generally likes to run at high RPM while a 4-stroke has more low end grunt. As for throttle response 4-strokes are great but your .46-AX should have near instant response too along with a nice smooth idle if it is tuned and propped right. The .55-AX has a power band somewhere in between a 4-stroke and a typical 2-stroke. It has more low end and will pull bigger props than the .46 but won't quite make as many RPM's. All are great and have their place. It is also a matter of finding what you like best for the way you like to fly.