There is also a very simple CG test that takes almost no effort. Simply fly the model past one way at speed, then turn it around and come back the other way. Only on the 2nd pass, fly it inverted. If it takes appreciable down elevator to hold the inverted flight elevation constant, there is a good probability that the model's CG is too far forward.

You don't have to trim the sucker for slow speed or anything. You've already got it trimmed for that "normal" speed and the elevator trim is either carrying a forward CG or not. And if you roll it over and fly that trim upside down, what does it do? It tries to lift the nose toward the ground and you have to push the elevator "down" to get the elevator to carry that forward CG. That forward CG is going to pull the nose toward the ground whether the airplane is right side up or upside down.

Simple and quick.