Any popular wisdom out there about rate of swimming in the pool and how it translates into rates of speed in the open water? I'm curious about how fast a person needs to be in order to do an Iron Man swim within the time cutoff.

Don't know if this is an answerable question. Guess I am trying to guage my pool speed and see if I am currently anywhere near the swimmer I would have to be to someday finish an IM triathlon.

Hope this isn't a dumb question. Thanks for any wisdom.