Many surfers have won Olympic medals for swimming, even though the reason they are so fast is because of the swimming practice they have gained from surfing. These swimming surfers could show their true abilities if they could also win medals in surfing.
For example, Duke Paoa Kahanamoku, the "king" of surfing, went to the 1912 Olympics in Stockholm, Sweden with the American team, and broke the record for the 100-yard freestyle, winning the gold medal. When it was time for the 1920 games at Antwerp, Belgium, Duke was 30 and too old to try out for the American team. But he whipped himself back into shape and broke his previous world record in the 100 meter sprint with a time of 60.4 seconds.
On the other hand the physical exertion involved in surfing would become less of a factor since there would be no need to paddle out through the current to the waves. Also, most surfers surf in salt water and the salt water boards are different then a fresh water board, so the movement of board could change.
Surfing should become a Olympic sport, I think the reason its not one yet is because people do not take surfers seriously. Most of the people who run the Olympics believe that ice skating or the high jump are real sports, but surfing is more of a sport than both of them and many of the other sports involved in the Olympics.