@romhackfanatic Yeah bangai-o stuttering is usually a lack of bios. You just need to download the dc bios, create a dc folder in retropie's bios folder, and then put dc_boot and dc_flash inside it.

Aha! I see it was failing to find the BIOS - I didn't consider that because literally every other game has worked perfectly. dc_boot.bin and dc_flash.bin were both in there, but they were the wrong files. Have now replaced them and everything's peachy. Cheers for the tip :)