My experience with abc, 2-stroke engines is to run them just slightly rich during break in, these engines rely on the engine getting to a normal operating temp. to properly seat the piston to sleeve, this cannot happen if they are to rich. I have always been told, and read, if you run them to rich they do not seat properly. My preference is to run larger engines on my planes mainly because I live at 6000 feet altitude and I like extra power for vertical, and I must admit I have used the extra power to get me out of trouble before. Although prop clearance can be an issue. Also if running a bigger engine take the pre-cautions to prevent control surface flutter I.E. seal hinge gaps, and use servos with more holding power. Having the servos in the rear helps with flutter
as well utilizing shorter push rods. I do not move my firewall back because if I do decide to go back to a 2-stroke, I do not want to add unusable weight to balance. I would rather move radio equip. or battery. Mentally, I find it easier to patch the holes where the servos were, than to ad weight. just another opinion. Sorry not to good with computers yet, I'm only 46 Garry