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: Red X Weimea SMaSH
Recent Meads: Mead Day '11 Ginger Metheglin, Mead Day '12 Traditional (orange blossom) Mead, Simple Cyser '12
Secondary: Why do I keep this line here...?
Bulk Aging: Cocobochet, Wild Cider, Simple Cyser
Planned: Hop Metheglin #3 (NZ hops), Trad. Gesho T'ej