The optimum setting is going to be the one that you set for the smoothest mode of operation. No one is going to be able to give you this information accurately without being there with the same unit.
Most important that you achieve a proper ground balance. You may need to adjust the sensitivity a bit for this to happen.
Start without any discrimination, and just dial in enough discrimination to eliminate the effect of the salt. Hunt in this setting. This should help you in the wet sand/water.
The XL Pro is a fast sweep detector. The faster you sweep it, the better it handles the ground matrix. This is in discriminate mode. In all metal mode it will work better with a slower sweep.
The above information is pertaining to standard operation in mineralized beach & the affects of salt.
Note: If your in a low mineralization area, and are just dealing with the problems of the salt, use the use the TR Disc. mode. If this works for you, this should produce the best results. You may have to refer to your owners manual to learn this procedure if you haven't been using it in the past.
Good luck with your hunt.