I ran into the exact same thing years ago, when I first started shooting clays. Stick with the 870 until you start losing birds because of it, or until you can afford another gun. It will do for now, if you are an experienced pump shooter (and I figure you are) you can shoot just about as fast as anything out there. But, an auto will have the advantage of lower felt recoil, and possibly a little quicker recovery, the O/U only has the advantage of shooting two different chokes for long and short bird stands. My advice is to save up and get you a Beretta 391, you'll love the gun, but shoot what you have for now.

Gordon