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Treefox you bring up the point I was going to make which is that you most often see TT athletes using a disc in the back and a trispoke or other slightly less aggressive wheel in the front.
This is because sidewinds hitting a front disc wheel can cause dramatic destabilization of the steering and make you crash. But as others have noted, if you want to take the risk and aren't limited by race rules, a front disc is more effective than a rear.