I can personally vouch for two comfortable bikes; the steel Trek 520 touring bike and the Titanium Airborne Carpe Diem cyclocross/Audax/Credit card tourer as Airborne calls it. Flaneur has already mentioned Randonnees; Audax is about the same thing where you need a bike you can ride for up to 90 hours at a time. Both bikes will have no problem supporting your weight and extra gear. They both have attachments for a rack and fenders which are often part of the comfort thing for me.

Forget the wide tires mentioned. They are not needed with a good frame/fork design. They also have way to much air drag if you ride above 12 mph or so and not to mention head winds. Both bikes can fit wider tires, but I'd go with something like 28 mm rear and 25 mm front maybe both at 25 mm.

I put together a Carpe Diem last summer. Very comfortable and very sporty. At http://www.geocities.com/cycleacrossusa/ you'll find a 3000 mile trip diary where a rider used a Carpe Diem. The daily average was 119 miles which is possibly a good indicator that the bike will be suitable enough for those triathlons and centuries. The Trek would be too slow for the triathlons I think.

Al