An ST4000+ or especially and ST4000+ Grand Prix should be more than adequate. I did a lot of singlehanded racing in the '80s with an Autohelm 2000 and cruised extensively in Mexico with an Autohelm 2000+ in 1999. The key as you would expect is in aggressively balancing the boat and sailplan. When off the wind the autopilot drove nicely with when wing and wing with a double-reefed main on one side and a poled out 150% roller furling jibtop on the other. I would roll a little jib in or out to fine tune the balance.
