I'm going to be flying the OS 140 in Advanced this year also. I flew 2 contests last fall in Advanced, and it pulls my 10 3/4 lb Eclipse fine. The 4 stroke does have more low end power, so it will accelerate better from low throttle, but that's just a function of the power curve on a 2 stroke vs 4 stroke. Some like one - some the other. I like a "simple" and reliable setup that won't need to be fussed with and won't make my Eclipse into a glider in the middle of a contest round. I believe that the YS DZ and the upcoming YS 160 have more power than the OS 140, but my goal is to have power AND reliability. When I go to a contest and see 4 of 10 Masters flyers (all 4stroke) deadstick in round 1 with various issues from broken internals to regulator and needle settings, I will vote for a little less power but relaibility every time. My motor has not quit in flight once since new (300 + flights) which is why I bought 2 more.