I'm sure that a smaller 1.2 FS or .90 two stroke would be adequate for sport plane use, but if you are competing, you better use what your competition uses. There is a tendency in competition, not just F3A, to blame the equipment though. A thousand buck investment in practice time, fuel, and possibly even a good coach, will do most people a lot more good than trading in last year's equipment in for the latest and greatest.