I went with a CS-M8000 (XT) 11-42 cassette.
Gaps between gears isn't an issue.
The first seven sprockets are the same on both the 11-40 and 11-42.
If climbing something which required 30 gear inches (30 front/28 rear) or lower then I'm looking for low gears and don't care about gaps. Bigger gaps just mean lower gears. I don't even think about it.
-Tim-