Elsewhere in the Forum RobbieW and Daria have commented on coppercoat .http://forum.oceancruisingclub.org/28-corrosion-a-antifouling/155-coppercoat-and-other-epoxy--copper-antifouling
We are certainly thinking seriously about it within the next year or two. We have friends that have had great success. Our boat, like yours, now has 6 seasons worth of Interspeed Ultra on it and I suspect all will need to come off in a year or two so that will be the time for us to take the plunge.
In the UK costs of hauling and painting are increasing substantially so it 's starting to look more attractive financially. The tests I have seen published aren 't very scientific but they do seem to bequite favorable.