A Large texture drawn in say paintshop, complete with roads, mud, grass, paths etc is then put on each quadpatch
Do you mean "large" as in 2048x2048?I don't know what you mean by this, you would basically have a texture with a bunch of different textures on it? wouldn't that just look like the same exact thing over and over (grass sand road; grass sand road; grass sand road etc..)?
OR are you referring to separate large textures for individual tiles? (I assume not, as you mention "complete with...")