there are 2 problems I notice when using the combat trim:
1. I get the elevator locked without warning.
When you dive, as the speed increases, the combat trim keeps trimming you forward. When you hit the compression you are already fully forward trimmed and need a long slow pullout trimming it back manually. If I have combat trim off, I'll be pushing the stick to keep the plane in a dive and get a quicker pullout.
2. Burning more E.
In turns, as I loose speed, the combat trim will trim me backwards and backwards. This means that I'm actually increasing the angle of attack even though I keep my stick at a constant position.
I suppose this is more of a personal feeling, but I have less controll of me E this way.
Both effects are on the player and not the flight model. you won't get any better preformance from trimming as far as I can tell.
Bozon