I've run engines from 20cc to 200cc, all of them got the longer arm. Granted some installations make this a bit more difficult. I typically make the arms out of fiberglass (G-10) or carbon fiber. A combination of a screw through the existing one on the stock throttle arm and a little JB weld keeps it in place. As said earlier, it's a combination of things that make the biggest difference, it looks like you are figuring that out. Have you adjusted in any right thrust yet. Video is an example of what is possible when you have everything right. Note the very small amount of rudder used in spite of the crosswind I had that day. This is a DA 150cc with a 1.75" throttle arm and 3 degrees of right thrust.