In the GPSAR program you can upload gpx files. Then you can get the spikes out (which I didn't do now) and get your polar of that day. (bases the winddirection upon the angles you sail around the course) This is ofcourse only a polar for upwind/downwind and not anything in between. I guess this will enable you to compare performance of a specific boat at a specific event.
Ofcourse windshifts, wind lanes etc. will influence one time off measurements as these.
