I agree that flight testing is the way to decide, but I do a different test. I trim to fly level, any speed, but I use a moderate cruise, at a good altitude. Note that how you trim for level flight will depend on where the CG is, but you will do it by observing the plane. Then put the plane in a dive and release the controls. If it is nose heavy it will pull out abruptly (because you would have needed a lot of up trim to fly it level). If it is close to neutral, it will just keep going down until you pull out. Theoretically it could tuck under, indicating that it is tail heavy, but you'd have problems long before you got to the test.
Most people like a little stability, meaning a tendency to pull out of the dive. Some planes I fly quite neutral, i.e., it goes where you point it, with respect to pitch.
There is a formula for estimating CG before you start. The factors are wing area, stab area, tail arm and wing chord. So actually, if you reduce the wing span the CG could go back a bit. It's probably too small an effect to be noticeable. And anyway, the purpose of the formula is only to get you in the ball park before you do the flight test.
Jim