I know I can do the distance - have done (one) audax fixed, but that was in East Anglia on no-traffic roads. Fixed + traffic = irrational fear. *Totally* irrational, because I rode the damn thing across London in rush hour and survived, so I clearly can do it. Just the thought of the first 20 miles out through the east London badlands makes me wibble, the rest would be fine. Going to do it anyway though :)