FWIW .... It comes back to the same old question: what do I want to do with your airplane.... I chose a Lycoming over a Rotax and a Rotec for my own reasons. I want to do long distance flying - I live in a big country. I looked at the Rotec because it (a) looked really good on this style of airplane and (b) because it is Australian made (I can be parochial sometimes ..). But it lost out primarily on profile drag and therefore long distance performance. I looked at the Rotax because it was lighter and lower cost than what I eventually bought. But I couldn't reconcile my concern about having a gearbox between engine and propellor, a higher revving engine etc. Others won't have the same concerns and in fact, I think the additional GB is less of an issue that I originally thought. For the R3600, you'll get more power with a higher fuel flow and higher drag. Your flight endurance will be down which means shorter flight times. But if that fits with how you want to use it, fill-ya-boots. In the end, I personally think a Rotec installed in a Kitfox looks really really good. But for my mission, it didn't fit the bill. That's my thought for today ....