Mark, no matter what you do... The snails will show up. Even if you removed every single snail, they will find a way into your pond. Every single pond I have ever seen, even those isolated by great distances from another BOW, eventually get snails in them.
When you restock your BG, add about 20-25% of the numbers as RES instead. They will control your snail population.
Ramshorn snails do get bigger and have harder shells than pond snails and the larger ones will not be edible by RES. I suspect freshwater drum would get large enough to feed on them, but as Omaha said, they are not available commercially. Plus, they are not native to our part of VA, so sourcing them from the wild is not possible. So, they aren't an option. CC will also eat snails and may very well feed on larger ramshorn snails.
I really wouldn't stress over this matter though...
