I would leave your top barrel in IM. If you can get a second shot in, it's almost always right at the edge of range. I like either knocking the bird down hard or missing it entirely with a long second rather than wounding with a loose pattern. For the bottom barrel, I used to go improved in early season and modified in late season, but I've been sticking with modified recently. I've got a bad habit of taking a quick, bad shot with my first, then a good shot with my second. For whatever reason, shooting modified first makes me wait for an extra half second so that I don't destroy the bird, then make a good first shot that hits the bird hard at ~25-30 yds. Lead out of modified more or less patterns like steel out of improved anyway. Also, pattern your gun with the load you'll be using. Black cloud, for example, patterns like IM out of my improved choke.