Thanks for all the great feedback guys. The mention of "404" and "training" together in the same message definitely stirs up some attention, I see. 🙂
To clarify, I actually didn't express a preference for the Zipp 404 recommendation or for the Alu clincher option, but just wanted to show you all the polar extremes of what suggestions I've heard. I actually just run cheapo Alex rims with 105/Ultegra hubs as training wheels, but after hearing that some were using carbon tubies as trainers, was curious as to what other TT folks out here are running. I appreciate the responses so far.
Regarding "potential", here's what I mean: I think that following (which I assume you mean as "studying", and not participating in) TT races is only a way to setup goals for yourself, e.g. if last year's Joe Blow did the city's main 40Km TT in 48mins, then a goal might be to match that, and to then beat that. However, it is in training and seeing what you personally are capable of, that reveals your own potential, e.g. it could be that you're only able to do the same 40Km in 55mins. You then train until there is minimal potential difference between yourself and last year's winner, and hopefully you can even surpass that level of performance.
Re: the comment about keeping consistent brake pad materials between training and race wheels, I think that's a great thing to aim for. Not too big of a problem as you could get another set of brake pad holders to save the trouble of swapping out the pads, but still, it's a convenience factor worth keeping in mind.
Re: using Gigantex or Cosmic Carbone SLs (clinchers): I've been hearing this one a lot too. The Cosmic Carbone SLs, being really Alu clinchers but with a carbon fairing, mean that they're tough enough for training but also aero enough for TT racing. Not the lightest, but that's ok for TT. A deep section wheelset you can train and race on is nice for so that, as the responder had explained, it gets you accustomed to dealing with crosswinds. As for the Gigantex, I'll need to look into what these are branded as here in North America. But, perhaps aero clinchers are still more durable than cheaper carbon tubies, is what I'm thinking.
Thanks again for the feedback so far, and I continue to welcome any further comments and personal experiences.
Note: fave story so far is a guy who was training on 404 tubies, hit a pothole that he couldn't see during a rainy day, broke both wheels, then picked up his bike and threw it. 🙂