For the floor? No, not too big. A recent tile trend has been large-format tiles in small spaces. I recently saw a beautiful model home with 24x24 tile in a secondary bath a lot smaller than your space. It looked great.

Less grout, easier to clean.

Our MB is tiny and the large format floor tiles we used look fabulous (IMHO!).

Larger the tile the more important a dead flat floor becomes. The larger the tile the more important that the file be of better quality and flat as lippage is more likely with the larger format tiles from everything I have read and been told.

It will look great. We have charcoal gray large format tiles in our MB which is about that size.

From a "looks" point of view, large tile is fine. From a "function" point of view, I prefer small tile because it's less slippery when wet -- and in a bathroom, the floor'll sometimes be wet.

Also, if you're going to the expense of marble tile, I'd rethink a white shower pan. The two choices don't seem to mesh. Yes, it's more expensive, but I'd go with an all-tiled shower.

Thanks for everyone's input. I am going to cut some paper patterns the size of the tiles and lay them out before final decision, but the pictures you shared have me leaning in that direction.

Second floor installation so just plywood subfloor---will your installer be using a waterproof system on floor tile as well as shower?