I went with a OS FS .72 four-stoke on mine. I had to put the batteries back close to the tail to get it to balance correctly, but it has got great performance!

I think I have had it for nearly 4 years, my flying bud and I call it 'old reliable'. It is easy to start, runs great, is easy to fly, and lands really nicely. I usually grab it on the way out to the field, because it seems like if everything else goes wrong, the SSE always works well(knock on wood).