Your milage will vary Some users of the US41 syncro conversion report power gains in the 200 rpm range, others 0 rpm increase, BUT both report much improved manners.
The variable may be the skill of the installer in setting the timing correctly
Using a spring starter with a CH ignition is VERY DANGEROUS, simply because a CH ignition will fire in eather direction. If you were not paying attation it can fire and jerk the prop out of your hand. Trust me that smarts, cause its going to wack you on the back of your hand.