Over/Under Pheasant Setup?

I love over unders :D. I'd say use the improved cylinder in the top, and the modified in the bottom. Shoot the bottom first, then the top. That way, when you first acquire your bird, you are probably accurate enough to hit it with a tighter choke, while on the second shot, you won't have as much time after the recoil hits you, so a looser choke will make up for that. All up to you though, personal experience gives the best advice.