Hi Bob, to be honest, I'm a little surprised myself that I can move the variable forward in 2nd as much as I have and still not hear the clean grain clutch slipping, but it hasn't yet. I have been waiting for it as I move that lever forward!
What problem did you solve with the filler bars? Was it over-threshing or incomplete shelling?
Funny you should mention the rubber concaves! I was just thinking about that this morning. As mentioned previously, I have a set of angle concave bars, which I think may be what is considered "half rounds". I was going to try replacing the channel concaves with those as a next step and see what happens.