Seems like overkill and over budget to me, unless you're trying to be competitive at 70.3 or Ironman distances. Polar says all of their monitors are OK for swimming, so long as you don't push the buttons while its underwater. My rs100 does just fine for me. I don't need the GPS functions, my cycle computer gives me enough info, and my wallet is more than $300 (which is half way to a nice used SS 29er) heavier than buying the fancy model.
As far as the triathlons go, be careful. You'll find yourself not wanting to do any other races anymore. Any plans for which one? Distance? There are some great sprint distance events around here, and of course St. Anthony's (registration opens, and likely closes, on Monday morning). Of course, since this is the Swamp board, I have to recommend http://tntraces.com/XTERRA_CALOOSAHATCHEE.html
. I'll be signing up for this one.