Im putting together a new 29" build for 2013 that hopefully will consist of:

Shimano 9070 rear derailleur
XX1 crankset with 32 or 34 ring
11spd 10-42 XX1 cassette or 10 spd Ceradure 11-36 cassette
Seatpost battery
TT shifter with custom clamp

Basicly im wondering if it is possible to:
a) run the 9070 derailleur with a 10spd cassette, and what kind of cage replacement it would need if any
b) fit a XX1 cage to the 9070 dearailleur to use a XX1 10-42 cassette

a) run the 9070 derailleur with a 10spd cassette, and what kind of cage replacement it would need if any?
won't work and its function of the cpu/ shifter not the derailleur.
b) fit a XX1 cage to the 9070 dearailleur to use a XX1 10-42 cassette?
not possible, and the issue isn't the cage in this case. Its the placement of the cage on the derailleur.

_________________
Rapha cycling's Ed Hardy

Closest thing you can do is get k-edge to make a ki2 using an ultegra rear derailleur. 9070 will not work with 10speed, but a 6770 rear derailleur on an otherwise 9070 group will shift 10speed. Ki2 conversion is a custom cage with a carefully placed upper pulley offset, and I believe at least one tension spring is different.

ok, thanks for input.

I guess it would be less hassle to do a stock Ultegra DI2 derailleur with a 11-32 and run a 2x10 front. Or could i get this to work with a 34 or possibly 36 cog?