The route through Germany is easy, the Polish stretch is dull and, depending on traffic reports, not worth taking the Autostrada (A2) from Poznan to Strykow - your 33zl you pay in tolls won't get you any faster than the old E30 that runs parallel to it, if there's traffic.
No no no, I don't recommend this at all. The section from Nowy Tomysl to Poznan is always busy with Polish trucks, and if you hit Poznan at any point between 6am and 10pm at night, it's going to be a drag through the city on DK92. The road surface is also absolutely shocking on the Poznan-Wresznia stretch - and is littered with traffic lights and 70/90 speed limits. For the sake of 33zl, it really isn't worth taking the old road - especially as it's got narrow lanes and is mostly single carriageway for the most part.
There's also the fact that (for the time being) the Kutno-Strykow section is free. The tolled part of the Autostrada is also quite empty and police rarely are seen on it - unlike on DK92.
The only bad thing about the A2 is the way that you'll have to stop every 40km or so for toll barriers, but there's never any queues at the toll stations.