Just though I'd post some pics of the new seat for those who are interested in a halo seat.
After trying several that didn't fit, I found the Pro ADV "just right" for my 5'9" 170 lb frame. I like that the halo tops out at about cheek level for me - does not impede side/rear vision. I also like that it has very supportive shoulder "wings", and that those are fairly wide relative to the waist. I can get out OK, but it requires that I take the steering wheel off, and practice getting the moves right.
Pics:
Old seat on the left (Cobra Suzuka S) - narrow in the shoulder vs. the new one one right.