For us, wind noise and the desire to stretch out are the two key factors that limit us to 100-150 km at a stretch (we are tall (1.95 and 1.8m) so more exposed to noise even wearing helmets) - after this type of distance we typically have a break and swap over which is a good safety approach. 3 or 4 of these stretches in a day is do-able if distance coverage is required but this is a touring car so enjoying places on the way is all part of the fun.
