The SD Association has this page explaining the speeds, and from what I can see, it’s just to guarantee speeds with certain bus types. Most devices currently use a UHS-I bus, and the older speed classes cap out at pretty pathetic numbers, so they’re kind of useless. For the steam deck, any of the higher-end cards are going to be about the same, and the IOPS are going to be more important in terms of loading times anyway.
Now what’s the difference between the 3 speeds?
The SD Association has this page explaining the speeds, and from what I can see, it’s just to guarantee speeds with certain bus types. Most devices currently use a UHS-I bus, and the older speed classes cap out at pretty pathetic numbers, so they’re kind of useless. For the steam deck, any of the higher-end cards are going to be about the same, and the IOPS are going to be more important in terms of loading times anyway.