The short answer, if I were beach hunting only I would probably go with the Excalibur, because you said you would be in chest deep water.
If it wasn't for the flooding problems it would be the Equinox, no question.
I've seen test where the equinox would detect gold chains better but haven't tested it myself.
The reason I quit using the Excalibur was that I hunted in pinpointer mode. I had to switch back to discrimination mode to check each target. The Excalibur has a weird discrimination mode that I didn't like. But I really did like the way that machine would sound off on a good target.
Before I sold the Excalibur I bought the CTX. I was very happy with that machine and didn't have any problems with it. It became my all around machine.
Then came the Equinox, after doing some testing against the CTX I sold the Excalibur and CTX. The equinox in my opinion could do most everything the other machines could do and I was able to put a couple thousand dollars back in my pocket.
But as we all know the equinox has its problems, but it's the best thing going for now.