It's only a question of density.

The modules with 512 MB and single bank have a higher density per bank, the ones with 512 MB and dual bank a lower density.
Some older mainboards couldn't address the modules with one bank (thus higher density) or they couldn't address more than 6 banks (thus if you have 4 slots and 4 dual bank modules only 6 of the 8 banks are recognized).
Furthermore the older Athlon 64 weren't able to address the memory at 1T if there were more than 4 banks so if you had 4 dual bank modules you had to decrease the timings, thus you had less performance.