Steve - what Jim wrote holds very true.
Many people, myself included, are very happy with the performance of the 4-stroke engines.
Others have tried them and just prefer the 2 stroke.
I have personally tried just about every brand of 4S engine on the market, reaching a conclusion there there are only three that seem to work extremely well for C/L:
ENYA, OS and SAITO.
If you want to stay small, the Surpass .26 is a fine little engine but, in my opinion, the SAITO .30 is the absolute winner in this size range. I have used it to power many .35 size planes - Nobler, Argus and the like.
I even flew my profile ARF Cardinal with it (a bit of a chore but it was fun). One now resides in my Argus and at around 42 ounces, the plane flies a lot better than I ever will.
If the .40 is your preference, the SAITO .40 and Surpass .40 are both excellent, the SAITO being a bit more user friendly for C/L, the OS a bit more powerful.
Next step up is the .46 size. There are three in this area: Surpass .48, ENYA .46 and SAITO .45. All sadly out of production. The ENYA .46 is the most amazing of the three. I truly believe it to be the most powerful of any engine - 2S or 4S in its size range. We've used it to replace a Super Tiger .46 and a Double Star .51 and there was no comparison. The OS .48 is just behind it, with excellent power. The weakest of the three is the SAITO .45. Silky smooth sport engine but down on power. It was replaced by the .50, which works very well.
In the mid-50s range, you have the ENYA .53, the Surpass .52 and the SAITO .56 - ALL EXCELLENT choices, in my opinion. In two cases, I acquired planes formally powered by the ST .60 and installed the ENYA .53. Both planes were in the 80 ounce range and the original builders, both top level flyers, agreed that the planes flew better with the ENYA. A friend of mine replaced a piped .61 with the OS .52 and was more pleased with its performance.
In the .70 - .72 area, we'll need feedback from others - my experience with them is minimal.
A word of advice - a few people I know purchased other brands of 4S engines. While fine for RC, they were very disappointed in the C/L performance.
Bob Z.