RE: ModelTech Sonic 500, need cg and surface travel info
Wes, 2 3/4" will be fine for that plane. I flew one for years, the O.S. AX is a great engine, we use those up here locally for our NCPL 500 class.
Give an APC 10x7 Sport prop a try on that engine. May not give you the best TOP speed, but it will take off like a rocket and accelerate like crazy out of a hard turn.
I ran mine with 3/16" throw on ailerons and a hair more on elevator on Low rates, but bumped each up another 1/16" for landing on high rates.
One of my favorite handling Q500 type planes. More of a fast Sport Plane than a racing plane though.