Boy did your thread get hijacked! I've been in similar conditions with my P19 and have found more speed upwind by flattening the main so much I thought I'd break something. And I did once. The jib halyard let go due to the weak brummel hook. I improved it with a very strong yet very small shackle(no halyard lock on my jib). The point is to use your legs to help you really crank on the mainsheet and downhaul-then pull out the jib leads. Once everything is tight and your sails are flat you can start to ease the traveller if you're still overpowered. You sound like you have enough weight out on the wire. Extend as much as possible and see what happens. The 18-2 is like the P19 in that the boards are small and you need to head down a few degrees to keep your speed up. As a previous poster mentioned-steering the waves correctly makes a big difference but it isn't easy to do.