Diki,

When you make edits to styles on SD1, they are transfered to the harddrive. No need to save to disk etc.. You have harddrive to store your styles , plus you can play the additional styles, directly from the harddrive. Midi midis are stored on harddrive,played from harddrive and you can edit songs while they play from the harddrive and save the song that has been edited, on the harddrive.
You can play your styles from your ram card & play your midi files from the ram card and you can edit your styles while they play from the ram card & play edit your midi filesin real time from the ram card... and that's good.
But I would still take the storage capabilities of a harddrive vs a ram card.

I guess that Roland is by far better with a ram card...