The eyepiece that gave me the most blackouts was the Explore Sci 40/68°. With an eye relief of 31mm, holding the exit pupil was very difficult, and eye placement was very finicky. Just too much of a good thing..
Diameter aside, SWA 40mms were fine there with a screw-up cup. I will buy an XW 40 first, the 30 if its OK.