Hello Konstantin,
With Amplify Texture 2 individual texture size is not a factor in the final performance, be it 4k, 8k or 16k. Go as high as possible, you can even take it one step further by combining large amounts of 16k textures into
Multi-Tile UV Collections. Regardless of the total amount of textures used in a Multi-Tile UV Collection it will be treated as a single texture by AT2, 1 drawcall.
When AT2 streams the data required it does so from a giant pre-processed virtual texture, the original texture files are not used.
Let us know if you have any additional questions, we would be happy to help.
All the best,
Ricardo