I've got Cosmic carbones too - fab wheels I really like them.
Is the TT bike for 10-25mile TT or for long distance tri? that might affect your choice if the former, you might go for a very steep seat tube angle and a disc wheel; if the latter a slighter slacker angle and not a disc would be better for all but the very best riders.
the PX is not especially steep but you can make it functionally steeper by having the seat forward and sitting right on the nose.
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