I did, if not the same, a very similar basket weave tile in our son's bathroom floor and shower floor. Seven years ago and I still like the look. I actually sought this style out after seeing it in a historic hotel.

I would recommend a medium colored grout because as you mentioned, there is a lot of grout and for a teen's bathroom, our light grey grout has discolored in the high traffic area.

For some reason, the sense of a weave gets lost for me on the jumbo and it looks like a marble field with small black dots instead of an actual over under weave pattern. But maybe I need to see a pic of it installed to get a sense of it better.

The smaller the tile, the less of the irregularity of the room, or the tile, are apparent. A large basketweave needs a super flat room, with a MUCH higher quality marble material.

81 SF is not a huge bathroom (not implying that it's small) - my bathroom is 120 sf (I feel it's a medium sized primary bathroom) - and I don't think a regular marble basketweave would be too small/busy in a bathroom the size of mine.

I do agree that the larger mosaic will make the different shades of Carrara marble more apparent than in a mosaic with smaller pieces of Carrara. That won't matter as much with some of the other types of marble because they don't have as much of a shade difference in the background as Carrara does.

I also haven't seen the large basketweave installed in real photos - I'd need to see it in order to really provide a fully informed opinion (vs. just my gut feelings).