We just went through this decision process myself last year. Some might argue that the latest hull shapes have a lot to do with the speed potential of the Formula 18s, but I believe most of that potential comes from the mast and sails. From the original Nacra F18 and Hobie Tiger, we've seen a pretty dramatic change in the mast weight and profiles that were coupled with sail design. I think both of these boats would continue to be competitive if they had the newer mast and sail design...but I don't think the math will work out in your favor if you include all of that extra cost.

That said, two of the boats on your list have seen only relatively minor changes from the older version to now and I think are the best value. The older Nacra Infusion and the AHPC Capricorn. Both of these boats have the latest mast and sail configuration and would probably just need a sail update to be completely competitive again. The biggest difference in these boats is the SLDBs (stupidly long daggerboards) which, in my opinion, add only very slightly to the boat's performance.