in triathlon (non-ITU) or time trialing, aerodynamics ALWAYS takes priority over weight, unless we are talking a very unreasonable weight (for instance buying a solid lead disk wheel).
Aerodynamics should be your number one concern because 1. triathletes try to hold a steady pace for a very long time, 2. triathletes cannot draft, and 3. most courses do not involve much climbing.
even for ITU though there are not really bad accelerations most of the time, because most triathletes are usually not very good at them anyway.
I would go for a minimum of a 50/90, and for a triathlete, well i would at least consider the 90/90.
remember also that pro's sometimes use a zipp 1080 front sub-9 rear which comes out to about 1700 grams.