That's a cool setup. I like it. Our tandem has a 12-34 in back and 52-39-26 in front. I run mostly from the 52. I hardly ever use the 39. Our 39 sees use mostly as a transition ring between the 52 and the 26. The only thing I don't like about our gearing is the 10 beat cadence difference when shifting in the back. PITA. You've solved that and good on you.