1 times 1024 is best. But if all those 4 textures are same 512x512 then that is best.
And there is nice method for square tiling textures, so you could use 512x512 texture to cover single tile, then make it differ frm tile to tile:
Make 512x512 greyscale mask with randomly shaded pixels, noise in photoshop does this i think.
Now scale this texture by 2,4,8,16 or any power of 2. You need 3 to 5 differently scaled masks.
You can rotate some of masks by 90, 180, 270 deg.
Add them all up, and divide by number of masks you added, so result is again in 0…1 range. (or 0-255)
Now you should have randomly looking mask.
Then use linear interpolate to colorize your texture. OR make 2 tiled textures and lerp between them with mask as alpha.
Your material should not tile even on big surfaces.