Wyeast recommends (among others) for a Wit their Belgian Abbey strain (1214), and for RIS (again, among others) their Belgian Abbey II (1762). This seems to be the closest comparable starting point for your search.
Both of these strains are rated to 12% ABV tolerance, which should get you the attenuation on the RIS you desire as long as your mash is fermentable enough.
Packaged: Fruitcake Old Ale
Primary: Simple Cyser '15
Secondary: Why do I keep this line here...?
Bulk Aging: Cocobochet, Wild Cider (2014 & 2015)
Planned: So many ideas, not enough time to brew them....