Different SD cards with different write speeds, perhaps?

Still, I don't understand why swp should play any role. Things are either in the RAM or in the swap. They should not be switching bewteen the two for hgih priority foreground processes.

Oh, I've just noticed: yes, my CPU ws also oveclocked to 900 MHz. To be honest, I assumed that that was the cause of the overheating so I reduced it back to 600 MHz but don't remember what the effect was since I no longer do big batch downloads on the device itself.