I'd agree with you and go for the performance. 8" of difference may enable you to miss a rock or two, but a 1' wave or a wake would remove that advantage quite fast, and you'd hit. You're certainly going to pick the same anchorages in any case. In the Bahamas there isn't a lot of tide. Being 400 pounds lighter, along with all the other go-fast gear, will definitely make a difference in how the boat reacts, and your the deeper, probably narrower keel will help improve upwind performance as well.
Of course, if you REALLY wanted to improve performance, you could have them get you a lead keel. THAT would enable you to reduce the wetted surface too, and not have to worry about rust so much.