Lehavre in France. From there i thought to break the journey up with even three stop overs, one in France, one in Germany.
I'd actually recommend doing Le Harve to Western Germany in one day (it's an easy run) and then stop for the next night just across the Polish border. That would leave you fresh to tackle the Swiecko-Nowy Tomsyl section of road, and Lodz to Lublin isn't so far.
An interesting alternative could be to head across from Le Harve towards Charleroi, going past Lille on the south side. Then Liege, Aachen, Cologne, Erfurt, Dresden, Gorlitz, Wroclaw, Krakow and Lublin.
This would have the benefit of spending the maximium amount of time on motorways, though I have no idea how it would compare to the Hannover/Berlin/Poznan route.