By the way you described it, you're using trim quite often, much more than I do.
I just use it when I am 1 on 1 with a plane. Right before we merge I trim it all the way up, it helps you loop better.
If you were a spit fighting a same model spit on combat trim, you would have the upper hand in turning if you trimmed it, but you still have a challenge ahead of you if it gets into scissors, because the trim can cause your nose to go up when you roll back over to stay on the 6 of the scissoring plane.
Another time I use trim is when I am in a plane, just compressed, and I dont want to hit auto-pilot because it may rip my wings off. I then trim it slowly until the plane is level again.
One of the last times I use trim is when I am in a plane that turns slightly worse than your opponant, such as a Hurricane IIC vs a Spit V. If I were the spit, I would trim up to get a tighter turning radius, and therefore almost equaling out with the hurricane.
You may also want to use it during a furball when you are in a turner, so you not only can outturn many planes, but be able to break away from attacking planes faster.