OS 4-strokes are EXCELLENT. I just got done bolting a .91 on my Skybolt. It started right up and sat in my driveway idling perfect. It runs smooth and seems to have plenty of power. That is on 10% fuel too. I know some people will say Saitos are lighter and have a little more power. That's generally true but I have experienced longer break in times on the Saitos and the need to run higher nitro (my .82 seems to like 20% for now). In my opinion, if you want a more user friendly 4-stroke, go for the OS.

The Surpass-2 line of OS 4-strokes has been out for quite a while. You'll notice that they now also have a .56 and .81 "a". These are slowly replacing the Surpasses. I can't wait to get my hands on an "a" model. The FL-70 is another story. It is an entry level engine sort of like an LA 2-stroke. I've owned a couple and they run great as long as you mount them upright or sideways. They have a carburetor that uses an air-bleed idle circuit that causes a lot of running and tuning issues when mounted inverted. Also you can't reverse the carb mounting on the FL so throttle hook up could be difficult on some planes.

For the Pulse, I'd personally run a 2-stroke. Either a .46 or .55 AX. I'm not sure why I feel that way, it just looks like a 2-stroke plane to me. A .70 or .80 range 4-stroke would definitely fly it well though, don't get me wrong.