It very much depends on your start time, whether you are working with vedette, randonneur or ciclotouriste time limits, how fast you ride and how much you faff.
For me, PBP99 was (roughly) 500 (Carhaix), 400 (Fougeres), 300km (finish) between sleep stops, though the unknown bonus 30km rerouting just before a sleep stop made that day tougher. 90hr start and <70hr finish. It worked well but being so focussed drained some of the enjoyment. Finishing in daylight became a priority for future PBPs.
PBP03 was a 90hr start and a deliberately more relaxed approach. Slept at Carhaix, Tintiniac and Nogent le Roi finishing in low-80 hours. Great fun.
PBP07 and PBP11 were both 84hr starts and the time limits felt quite restricting until the last 150km or so, when they got very generous. Sleep stops were ad hoc locations (all but one in PBP stops), and always restricted by time limits. Weather and other factors meant I never covered the distances I expected to do each day. Sub-80hr finishes.
I'll be in the 90hr start next time and aiming for a <90hr finish.