6870 Di2 rear mech on 10 speed cassette?

Cyclosis
Cyclosis Posts: 35
edited January 2014 in Road buying advice
Hi Folks,

I'm having trouble getting a 6770 rear mech for a decent price — across the board it's about £20 more than the 6870!

Anyone tried running the 6870 on a 10 speed setup?

It would have me some dough upgrading to 11 speed later on too.