Speaking of combinations that shouldn't work:
I used a 30-43-50 with a 14-28 rear shifted by Campy Super Record rear and flat slab Record front derailleurs. I just made sure to never go to the 30-tooth ring unless I was in the 24 or 28 on the rear. Because the rear derailluer has a stop to limit the cage windup, I could get away with using a lot of chain. It would just hang slack if I used the 30 with any of the smaller cogs. And yeah, I know the 43 was not the ideal middle ring. I think out of a theoretical 18 speeds, I had seven discreet gears, but a couple of different way s to get each one.
Earle Young
Madison, Wisc