Look:

http://www.analyticcycling.com/WheelsConcept_Disc.html

Difference between deep rim wheel and disk is less than difference between standard wheel and deep rim.

So in real world, a disk wheel gives an advantage of a couple of minutes over and Ironman distance. A worthy upgrade if you are losing your age group by a couple of minutes. Otherwise, save your money, hire a coach and train more.