Also with a 50 on the front and 11-36 cassette you can basically ride it on the big chainring most of the time and only use the 34 for climbing proper hills. Then you won't be needing to use the small-small cross chain combinations.
It is worth persevering with the Di2. Sure you can trim you 8sp to perfection but with the Di2 set up properly it will be right all the time with no trimming required.