By my experience, this is what runs GOOD:
GameYob
QuickNES Retroarch
BlargSNES
Pokemini 3DS
NXEngine Retroarch
Other things i tried:
mGBA - It DEFINITELY doesn't run well
FCeumm Retroarch - 50% speed
Ganbatte Retroarch - 70% speed or so. Maybe more. Not perfect, that's for sure
Wanna try more this week, maybe Picodrive as you mentioned earlier?
Picodrive is a work in progress. There's some stuff playable, there's other stuff completely not playable and there's stuff in between.
But according to the latest reports (haven't tested yet), it seems it's improving with each update so I have hope that it will keep improving.