Power Meters / Powermeters (SRM, Powertap, Quarq, Ergomo, Vector, Stages, power2max, P2M, 4iii, InPower, Cinch)

Essentially i think i want to find out what my FTP then apply a formula to that to work out what output i should be aiming for a 100 mile TT and then another reduction for 112 miles with a marathon to do afterwards...

You'll be looking around 70-75% of FTP for the bike course, I believe.