What're the technical differences between the Gold Cup line versus the regular A/O line?

Hi, The Gold Cup line is a higher end line for Sperry. The come with memory foam footbeds, lambskin linings, extra cushions in the midsole, rust proof gold eyelets and premium leathers. The standard A/O line is premium leathers, cushioned footbeds and the A/O slip resistant outsoles. Please let us know if you have any further questions. ShoeZen

I've had deck shoes; some are cushioned and comfortable and others feel like I am walking on a sidewalk barefoot for hours. Are these comfortable?

These ones are definitely cushioned and comfortable. I own pairs of both kinds but these shoes actually feel like they were meant to take good care of your feet.

I take a 9M. If the width isn't specified, can I assume it's a medium?

I wear size 11 and they came as medium. I went on the website and noticed that some sizes also came as wide. I think that the default width is medium but I am only assuming that, I'm not sure.