What's the maximum terrain texture size?

I currently have a terrain grid of 4 x 4 tiles that is 65840 meters on a side with square tiles that are each 16460 meters wide and have a 2048 pixel texture map.

I now want to create a terrain the size of 1 of these tiles, about 10 miles wide, with maximum resolution, tiling as necessary. Is 2048 pixels the maximum resolution of texture map I can use and then tile to get the size I want?

I'd tell you to use the terrain toolkit for texturing instead of his method, but the proceedural texturing stuff doesnt work above 2048. I have another question addressing this, though.

I believe if you look at the texture import dialog (select a texture in your project and look at the inspector), you can set the imported resolution as high as 4096, but then you're putting a lot of faith in players' graphics cards. I'm also not sure if there are any specific limits to the Unity terrain tools themselves.

I'd say go with your notion of a 2048 tilable texture. If you want to get all professional about it, do up a shader or material stack that can take multiple textures to tile and multiple grayscale textures to mask. Each mask can stretch across the entire terrain, if it blurs, that's fine, because all it will be doing is telling the shader how much of the corresponding tiled texture's color to blend into the final plane at the given point.