Just so you get a different perspective on this, mine would be that with the Hobie 18 Magnum, you need as much power as you can get. You should shove your battens in until the sail looks like a hungry dog. Fuller the better.

We have seen too many people get discouraged and leave sailboat racing because they listened to the flat-sail theory when it is not the best theory for their particular boat and/or their particular weight or the sailing conditions where they normally sail.