Basically, can I mix a mountain Di2 rear derailleur (specifically, the RD-M8050-GS) and with a road Di2 front derailleur (specifically, the FD-R8050)? Will firmware updates and syncro shift still both work properly?
Full context: I'm trying to build a touring tandem with a very wide gearing ratio... hoping for an 11-42 tooth cassette and a 16 tooth differential in the front.
I'd use full syncro-shift to ensure I can't cross chain (at least after it finished shifting) to ensure the rear derailleur has sufficient chain wrap capacity.
The other option is to use either (1) all mountain derailleurs with a larger big chainring at a 16-tooth differential, but I understand the front XT derailleur is only supposed to be used on a 10-tooth chainring differential, or (2) all road derailleurs with an 11-42 mountain cassette, but the road rear derailleur is only spec'd up to a 34-tooth sprocket, and I'm not sure if a road derailleur with a Wolf Tooth RoadLink DM (to allow bigger cogs) is as good as a native mountain derailleur on an 11-42 cassette.