Without some serious cash (and about 100 extra lbs), you really have to race your boat repetitively to get a feel for how your speed is. Use your recreational time on the water to practice tacking and gybing as well as starts and mark roundings off a bouy. 50% of any speed you have on the race course will be lost performing these manuevers because mistakes here cost you dearly. Then on the race course you can really focus on boat speed with your competitors because your mechanics are good and second nature.

On big dollar yachts, they will have wind direction, wind speed, current speed, current direction (bottom sonar), hull speed, and heel all tied into a computer that can give them all sorts of information about their sailing efficiency.