I have shot both the 11-87 and the silver hunter, both top notch guns, the Silver hunter is a very smooth gun liked it alot, great cycling gun. the only complaint I had with the Silver hunter was the over sized forearm on it, it just didn't feel right to me.

A Remington is always a solid gun as you know with your 870, very nice gun, smooth, you can swing it alot easier, I found it to be a little on the lighter side. I have always been a Remington kind of guy, I have both they 11-87 and 1100 and they only guns that came close to making me choose otherwise would have been the Browning line of guns.

Either way you have narrowed it down to two fine guns and whatever you choose will be an awesome addition for duck hunting. Good luck and when you get it post pictures I would like to see it.

I really don't know anything about O/U's so I will let someone else tackle those for you.