There is another alternative to reciprocating piston engines other than turboprops, the modern rotary engine as developed by the swiss company Mistral Engines
http://www.mistral-engines.com/. They are perfectly suited for GA with 200 hp to 360 hp. The mistral engines burn leaded/unleaded fuel, avgas, mogas, even ethanol containing fuel. It has already flown in a Maule and in a Piper Arrow. Mistral will be exhibiting their engines on the AERO these days at Friedrichshafen and I'm going to visit them at their booth. I will be posting more when I've got more recent info on their status.