My brother and I have switched over and now run four strokes on almost all of our planes.
(1) 61, (3) 70's, (6) 91's they are a mix of OS and Magnum.
We have never even checked the valves on any of them and unless one of them gives me a reason I don't plan to.
I used 10% fuel for the first couple of years and was completely happy.
Then we got a deal on a couple of cases of 15% fuel and we got a 700 - 1000 rpm increase depending on the engine.
I didn't expect the power boost but it was a very nice bonus and I will stick with the 15% nitro.
I use a tach to set the high speed needle and check that setting every 3 or 4 trips to the field.
These engines have all been great performers, very reliable, the only deadsticks i can recall were caused by a clunk being stuck and a cracked fuel line.
I see a lot of people constantly fiddling with anything that can be adjusted and they always seem to be having problems.
We try to set them up carefully the first time getting the low end needle set so the idle and transition is excellent, after that we pretty much leave that part alone.
If we are flying a lot we don't mess with the high end much either.
When we were using the two strokes we pretty much followed the same pattern.
The Magnums have worked very well for me, if I was making a recomendation on a "first" four stroke I would recommend OS.
Oh yeah, an electric starter is an excellent investment.