HELP, TRi bike riding vs road race

Your legs will feel better and you will be better off for the run if you have a higher cadence on the bike.  Higher cadence will equal higher speeds with more time in the saddle and gaining overall leg strength.

I'm not sure I understand the question, but compared to road racing the bike portion of a tri is much more of a constant effort.  You can't conserve energy the way you do in a road race, but you never have to do sprint either, so you can use a fairly high cadence but always have some pressure on the pedals.