Not effect the output quality, but to effect the output quantity.
My personal visualization of this is that Q10 kilns would produce 80, Q40 would do our present 120, Q90 would produce 180.
Also it would increase the tar output.
Given that Q40 clay is relatively trivial to find, most people would be able to manage standard Tar Kiln operation with a little effort, while those capable of finding Q90+ clay would be able to make their High Q wood stretch a little further.