Having both, and enjoying both I don't see any difference between them for upland game or actually any other shooting. However, call me a hopless romantic, but I like the way a good SxS feels in the hands. If I had to choose between the two, I would have to pick the SxS.

Here is my choice.

anybody know anything about the mossberg o/u?

I Have both, love the SS 28 ga. over the 12ga. OU. It depends what you like, try them both.

A little overkill aint it?

The Silver Reserves seem to be great guns for the money in my experience with them. While that experience is quite limited, the handled extremely well. I only shot the 12 ga. O/U model.

Close up it can be. But most of my shots aren't too close.

I started hunting seriously when I was abot 12 - 1960's. I lusted for a SXS, and finally scraped up enough "hay baling/corn breaking/barn cleaning" $$$ to by a used Ithaca "Nitro Special" from a neighbor. I used this shotgun for decades on everything from rabbits to geese to deer. And O/U probably has a lot of advantages over a SXS, but I am too old a dog to change now ! I love 'em.