I purchased my P19 in 1995 and upgraded it to the MX 5 years later. The MX sails were from Ullman via Jay and Pease Glaser. They were very helpful with tuning information. The boat is quite a bit faster downwind in the MX configuration. Upwind the squaretop main is more forgiving as it twists off in gusts. On the downside the larger headsail sometimes gets caught on the wishbone for the mast rotator if the crew doesn't handle it correctly. You have to install a "jib pole" to support the deeper foot of the jib. This pole allows you to mount a windex on the end. This helps a lot in light wind when you sit forward of the mainbeam to keep the transoms out of the water. I highly recommend going for the MX upgrade. Very few non-spinnaker boats can keep up with you downwind in a breeze.