4 strokes are cool sounding. They are more expensive however, weigh more and there is more to maintain.

I've flown my Tiger2 and Calmato with both the 46AX and 55AX. I doubt anyone on the ground could tell which engine was in the air. About the only time I noticed was on straight climbs. They really don't happen too often. And even then, the 46 has absolutely no problem with tear drops, humpty bumps, or anything with verticals.

I fly 5% nitro in all my glow engines in the winter. In the middle of summer, I'll usually switch over to 10%. When it gets real hot, I'll use 15% or if I'm visiting a field that's in the mountains. Nitro provides oxygen. It also burns with less heat. It's better in the summer than low nitro fuel for helping the engine run cooler and with better power. It's not needed in the winter. There is no real magic to fuel brands. I use Omega with and without castor. With castor in the summer when it's easier to fly with too lean a needle. But it's not a big deal. Synthetic fuel is cleaner and provides excellent lubrication. I make sure to run some synthetic every so often in all my planes to help clean out the castor buildup. Also not a big deal.