Soldato
The Di2 on the Tarmac was all 7100 series (new 105 SD300) with just a 8100 crankset, my older 11 speeds are more mixed... But that's the beauty of 11s Di2 SD30 - you can mix & match! You can't tell me all of your groupsets on your bikes are all the same series, including cranks and cassettes?! Especially with any off the shelf bike. Look closely at model numbers, I bet most bikes spec as Ultegra are using some non-series or 105 parts
Erm. Mostly. Well on my Ican bike anyway since i built it with a Sram Force groupset. Although i did go with a rival cassette as i think it was meant to be harder wearing (and cheaper!)
My Trek MTB is a right mix!