I’ll let you know once I get more info on the new 12 speed stuff, existing 105 Di2 run 36t max capacity, which mean a theoretical 46t cassette with 12 speed 46/30.
Needs to be tested, by looking at it doesn't really look there's more capacity in there than the old Ultegra RX/GRX double,and less choice of cassette sizes
I’ll let you know once I get more info on the new 12 speed stuff, existing 105 Di2 run 36t max capacity, which mean a theoretical 46t cassette with 12 speed 46/30.