RE: Recommendation for slugs for Remington 11-87
I would try something in the velocity range of 1300, 1500, and 1700-1900.
My marlin 512 hated the Hornady H2k. But it shoots awesome with Winchester's cheapest sabot, 1 oz. @ 1350 fps.
You really do have to try a few brands. If you plan to do this all in one day, think about a partner (if you know someone that can shoot well) to do some of the shooting. You may try the slug the gun likes best last, but by then you may be flinching (the dreaded f word).