depends
I have a 28.5 and have sailed the boat in 3 different locations. Chesapeake, Lake Erie and New England. On the Chesapeake I could of used a driffter, Eire the 150 was useful and here in New England the 150 is too much sail most days. I origianly had a 155 and I found it difficult to trim. The slot was too small. What type of wind condidtions do you normally sail in? Do you have a roller furling? If so you could easly reef the head sail on the furler and have the best of both world. As for the cost. Go to sailnet.com they link up with airforce sails and give you prices right on line for many boats. I would suggest that you talk with your local sail maker and give them a shot. For a little more money you will have the opportunity to have your sail made with local expert advise and you can usally get a few coaching lessens on how to trim and sail you boat more efficent.
