I see plenty of replies to most your questions, accept the "4 stroke verses 2 Stroke" .
I am not experienced enough to comment on Yey or Neys of these motors but will tell you I bought the Siato 4 stroke .71 for it's classic "Tone" and Luggish sounding nature for my Balsa Piper J3 Cub.

I wasn't concerned about horse power and if I noticed anything at all it is that,
IF YOU WANT POWER, low cost and low weight buy a 2 stroke, power for the dollar they beat all, My hyper 50 in my Raptor helicopter would smoke the .71 Siato, but I didn't want power this time around for the Piper, I wanted a good "Tone" large Prop and lower cruising rpm to give it a scale like look, feel and sound. As for what’s the "Better Engine"? I can't dog on 2 strokes because so many of them are running like a million dollars worth compared to yesteryears motors. My Hyper OS 50 starts right up with a slow running 18 dollar Wal-Mart electric drill. I f you don't care about Tone or are wanting a ripping high performance speed demon I would go with the 2 stroke for the lighter weight and more power at a lower cost the 2 strokes are notorious for. My .71 Siato has no more Horse power than the .46 2 strokes out here. But it sounds like a mini Harley under my Cowling. ONE more thing, I personally think a "Ringed" piston is better then a butt naked one regardless of how many strokes.
[8D]