Recommendations for a dual prupose high grav yeast

I've decided my next two brews will be as follows:

First, a very drinkable run of the mill Wit.

Second, a big Russian Imperial, Beersmith puts my recipe at 1.111 OG, 1.021 FG (maybe a little optimistic).

Plan is it rack the Imperial right onto the cake leftover from the Wit to get it kicking ASAP. So I'm looking for a high tolerance yeast that will make a decent Wit and a good stout in high gravity.

Any recommendations?

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.