i wouldn't take too seriously what most people say about tire width and performance. especially since it is so easy to make a reasonable determination for yourself.
i imagine most triathletes have various timing and distance measuring equipment, so what i would do is map out a rather flat, wind neutral, low-traffic, minimal stopping route. maybe even a park setting. set a heart rate target and keep it for a specified time interval. when done. see how far you have gone. switch tires and do it again sometime under similar circumstances. maybe a few times, then average and compare.
i like this approach because i wouldn't have to take some internet strangers hearsay advice.
BTW, before someone beats me to it, this applies to me too.
