> If I remember it correctly, the MPC5121e offers no superior [...] cache
You don't: https://morph.zone/modules/newbb_plus/viewtopic.php?topic_id=6176&forum=11#61282
> nor interfaces (well, there's SATA and better USB).
And you don't think SATA and better USB are superior to PATA and slower USB?
Besides, the MPC5121e is 2-way superscalar (dual integer units in the e300c4 core), while the MPC5200B is non-superscalar (single integer unit in the e300c0(?) core).