Here is a link that is informative. It sounds like you can do 1/16". the tiles need to be very precisely sized with this small grout line according to this reference. The grout will need to be unsanded at the 1/16" size. Sanded grout is used for larger spaces of 1/8" or greater. Here is a link that might be useful: Tile Council of North America site

Clickhere then scroll down about half way and start reading. Before any grout width is determined, the overall flatness of the tiles must be tested. This varies from batch to batch. The more pillowed the tiles, the less the offset (as noted at the bottom of the manufacturers' link you provided) and the wider the grout joint. Also - The substrate flatness for tiles of this size needs to be no greater than 1/16" over 24 inches and 1/8" over 10 feet measured peak to peak. Click here. If you have grout color concerns, use Flexcolor CQ, Plasma, or Fusion Pro and have no color or staining worries.

Don’t do it. You will have issues with uneven spacing and lippage.

Agree with Mongo that you should consider a more rectified tile. Any variation of facial dimension or wedging will impact how closely the tiles can be aligned and yes, must be compensated for by a larger grout joint. We like Adex Neri tile for this purpose (as ONE example), and while not available at big box stores, it is not an expensive tile AND (very important for us and our clients), it has many finishing pieces available for a very tailored and custom look. Here's a link to Adex: http://adexusa.com/portfolio-item/adnz836-neri-field-tile/ Second point, the grout selection must meet the specifications for the tile and the installation. It is true that sanded grout requires thicker grout joints, however there are newer high performance grouts specified for wet areas AND can be used with 1/16th grout joints. There are several but we prefer Laticrete PermaColor and they also have a Laticrete Select specified for this application. Here's a link: https://laticrete.com/~/media/marketing_information/permacolorsellsheet.ashx Obviously the surface prep is important for any installation to obtain a flat and even tiled surface. Keep in mind that professionals will have different products they are comfortable with. Specifying a 1/16th" grout joint is not unreasonable for your installation as long as the tile you choose is appropriate (flat and rectified with minimal facial dimension and uniform size), the appropriate grout is used, and the installer is qualified (as Mongo stated). That being said, we have never installed a subway tile with more than a 1/16th" grout joint. Our clients, like you, would never accept the appearance (nor the excessive maintenance). Here's a tub surround we just completed with Adex subway tile, 3x6. Good luck with your project.