Mtn Bike vs Tri bike my experience.

I posted last year a question about how much a tri bike would improve my time from the mountain bike. With all the responses I received I would say the consensus was about a 3mph improvement. So I decided to take the plunge and purchase a tri bike. This past weekend was my first race with the new tri bike, and just happen to be the same olympic distance race I did last year on a mountain bike. In comparison I put in equal training time, drills, same body weight etc., and the only difference in the race last year was the swim was cut short due to weather. So I would say most variables would be comparable and the results are.
Last year on the mountain bike (gary fisher, 1.75 tires)I averaged. 19.5mph , and this year the tri bike(entry p2sl) was.. 22mph. Outside of the obvious speed difference, I was less fatigued in the shoulders, back and overall. In the end I am happy with the results and now focusing a bit more on the bike training and hope to get a couple more mphs. Just thought I would share this little experiment if there was anyone else in the situation as I was last year.