If you're alone in the duck blind, I think an O/U works fine. However, depending on the blind layout, if you have fellow hunters, a normal barrell length (26-28") can cause some noise issues... especially if it's ported.

Since you have three duck guns already, why don't you go get a 16/20/28 O/U for pheasants and other upland hunting. In your price range there are a lot of options. I think you're right on track. Have fun.