I think a honed carrara (or similar) in a 3 x 6 or 6 x 12 inch subway style tile with a honed carrara base would look smashing...I'd use this as the shower floor as well if it were me :)

Sarah, I am going to use this as floor tile, what would you suggest for the shower wall? I am thinking a dark floating vanity and a soft grey paint...struggling with the shower - do I want detail or keep it simple? Value your opinion.

Depends on what you do with the shower floor...if you used a simple gray mosaic in the floor you could do panels of this pattern on the walls outlined in a nice molding. If you use this pattern in the floor... You could still change texture inside panels or between moldings applied around the shower at different heights--up high even. Am I making any sense? Shower walls can be boring if there's no texture or material change within them...