I've done it, biking home, from Brielle (NL) to Erfurt, 650 km in 4 days. Here are the stats and figures:
Day 1: Brielle - Venlo (210 km)
Day 2: Duisburg - Soest (130 km)
Day 3: Soest - Göttingen (170 km)
Day 4: Göttingen - Erfurt (140 km)
And, as a result of this, new wheels are needed. My ones broke down and were not able to handle the pressure :)