From a gear standpoint, I've kinda done the top things to shave minutes: Aero position, aero wheels, aero helmet. The other upgrades (bearings, cranks, carbon wing uber-bars, all that crap) are a big cash outlay for saving seconds.

And the biggest speed boost I've purchased for tri? A good wetsuit. No question.

That's more than enough bike for a schmuck like me, and gets all the big benefits. Once I have 1. a lot more money and/or 2. a much faster engine, I'll shop for the lots-of-cash-to-save-a-few-seconds upgrades.