Angelo mentions some good things to look at. On reading the OP, my first thought was
jib lead locations and my second was position of the traveler for the main's angle and my third was was whether pulling the vang down to flatten the main would provide the improved speed and improve sail shape and reduce weather helm.
I seem to recall a book that I have stuck away somewhere which is a collection of articles from SAIL called the The Best of Sail Trim (or something like that) that covers sail shape and speed for all sails and conditions. It was worth looking at - some review, some new stuff.