What is the concensus on the optimal cadence for a 40K TT, and how might this change when looked at from a pure cycling point of view to a Triathlon point of view?

Does riding an easy gear at a higher cadence have less impact on your legs than riding harder gears at the same of even lower cadence? Does this mean that riding easy gears at higher candence will help you on the run?

And if it help you on the run, does it hinder you on the bike - what you gain on the run your more than loose for on the bike?