Hi Paul, welcome to the forum!! It sounds to me like you've done some reading here (and maybe at www.poolsolutions.com) and have a decent 'grip' on what's going on with your pool. At this point in the season, waiting til spring to make major chem changes is probably the best idea.
With such a high cya level vs cl, you may expeience some algae when you open the pool next spring, however - this may help bring the cya level down. I don't know if it's more cost efficient to partially drain a pool to rid it of excess cya or to let the pool become an algae pit (which also seems to deplete the cya), perhaps someone else could perform the 'cost analysis' [too many variables for me to calculate].
Whichever way you go (drain now or wait til spring and possibly deal with cya reducing algae) - I'd say let the pool 'sleep' for the winter and DEFINATELY make the change to BBB next season and never have this conundrum again

Just my] take on things! Again, welcome to the forum, and if you need some help in the spring 'getting things right', all you have to do is ask and we'll help you! - Waste