My thoughts too. No sleep deprivation in a marathon.LEL and PBP I regard as being more equivalent to those Ultra-Marathons where they run the entire length of the Pennine Way or similar. You don't have to take a nap at the side of the road for RideLondon or the London Marathon!
Difference with a bike is the opportunity to freewheel downhill for 'recovery' and body weight is supported by a saddle. I used to work on 3 miles cycling equivalent to 1 mile running - using that 'rule' 75 miles would be equivalent. From experience I would need as much time to recover from a 100 mile road race or 300km Audax as I did from running a Marathon.