Which Groupset?

11-32

This was a Leonard Zinn article I remember on hacking Di2 a bit to get a 32 on it

Another option might be to try a Shimano cogset not recommended for Di2, as a number of riders used on the Angliru climb in the Vuelta this past season. (The maximum cog size recommend by Shimano for Dura-Ace Di2 is 27 teeth.)
I’ve heard of riders using Shimano cogsets topping out at 30 or 32. They said that they had to max out their b-screw adjustment (to rotate the cage way back so the upper jockey wheel won’t pinch the chain between against the largest cog). A trick for getting more backward rotation rear derailleur rotation to eliminate noise and roughness on the largest cog is to remove the b-screw and put it in from the opposite direction so the head, rather than the tip, contacts the derailleur hanger tab. You have to be very careful when trying a cog larger than the recommendation, as you wouldn’t want to ruin such an expensive derailleur by trying to make a shift that it couldn’t handle because the chain was too short.