@retroman Hey! Do you mean of the Amazon cards? I've actually found that the 128GB model I have is slightly slower in most areas than the 64GB cards, so it's the 64GB one I recommend in most cases!
I wouldn't be able to say where the difference is exactly, I use the same microSD card on the board and they're all just blank cards with an ext4 filesystem on them tested in exactly the same way. I'd have perhaps expected both of them to be closer than they are but in the boards I've tested with the 128 so far (I only picked it up over Christmas) it's been consistently slower than the 64 but still very good overall.