I've landed a Saratoga on the beach at Barra. Fantastic experience. Allow 40 mins after the tide for drying and its firm, no problem at all. Be a little conservative with winds as the surrounding hills can give up and down draughts on approach, particularly on RW 17. I had first down-draught, then on short as I was trying for the threshold, an up-draught - not very helpful. I would suggest a limit of 15-20 knots.
Remember to depart before the tide comes in. It is possible to pull your aircraft onto the shingle above the waterline, then you have time to explore the island and stay overnight. Your'll need some boards to run the wheels on and tie-downs. Tanker fuel.
Consider to first land at Oban to phone for latest information.
Go for it.
flyme