I don't know. I have only ever shot slugs out of cylinder and imporoved cylinder. Since no one posted, I can tell you that I did a Yahoo search and found a few barrel and shotgun manufacutures recommending improved cylinder for slugs. In the scheme of things, an improved modified is significantly smaller than improved cylinder.
BTW, your garden variety slugs, like Remington 12 ga. 2 1/2 inch "slugger" shotgun slugs are rifled slugs. A lot of people call them Foster slugs. Remmington "Buckhammer" slugs are entirely different, and are not rifled, thus you'd do better with a rifled slug barrel. I've seen rifled Foster slugs sold as hollowpoints, but that doesn't seem to mean anything, since the Foster slugs I've recovered from game squash instead of mushroom.
What about using 00 Buck for coyote? I don't hunt anymore. I only once went coyote hunting, and no one got anything. I took an 870 with 00 Buck. I don't know what your local laws are as far as coyote, buckshot, and shooting coyote while turkey hunting. Where I was, coyote weren't protected anyway.