I endorse an earlier comment along the lines 'do we really need a Gigabyte SD card'?
I'm using a 256MB card , have all the styles I can find plus midi's, and I have only used 111MB.
I do not have any MP3's onboard and that could make a difference. But even so I would think that 512MB would be the largest one would ever need.
Though I do recall comments of 10 or more years ago that 64MB on a PC would last forever!