the answers all just prove cougie's first statement that you shouldn't try to compare. everybody is different.
eg punchy says a 100 mile ride in 5 hours is the same as a 4 hour marathon. personally i would have trouble running a marathon that slowly (except in an ironman, of course!!) but i'd have to push moderately to maintain 20mph on the bike for 5 hours. So for me, I guess that a 100 mile ride in 5 hours would be the same as a 3:20 marathon.
it depends which you are better at. no point trying to compare.
