You are exactly right, but buy a sport flying plane for sport flying. Remember, this is the 3D forum, not the sport flyers forum. He asked the 3Ders opinion. And I told him that at lower elevations the 72 is fine. I said stay away from the 80 due to the POWER TO WEIGHT RATIO. Yes it makes good power, but not for its weight. Not as good as the 72. and I say if you are gonna add 3 oz. you might as well add 2 more inches to your prop size rather than just swing the same prop faster. Also RUMPLE, you are absolutely correct. The 100 is ballistic power. But the way I see it, the 91 is almost as ballistic. This is what I think. Living where I live, If i where to buy a engine for a funtana, like I said earlier, I would buy a .72. It would work for me as well as most of the people in the US. If I lived at a higher eleveation, I would probably buy the 100 over the 91. Mostly due to the fact that they weight the same, the price difference is only a few dollars and the 100 makes more power. Thats it.