Personally, I'd leave the stock coil on and see how it goes. May not be enough trash in that area to warrent the smaller coil. Plus, it's a lot harder to cover such a massive area with the smallie. If you run into a snag with the larger one, slap on the little guy. Just my opinion.
I have a 250 and use it in the dry sand all the time. It doesn't do as well in the wet sand. I get alot of weak signals that like to disappear in the wet sand but the coins will still ring loud and clear.