Thanks for everyone's input. At the end of the day, I think I'll stick with the FD for as long as it works, then jump to the 6603 STIs. In the meantime, I'll try to just focus on the cadence & leave the gear map to climbs. As for my LBS, we're his only tandem business. He's still races (road, cyclocross, & crits, albeit in the 50+ category), but I don't believe that he's ever been on a tandem.