But you can only go so far with a flat-plane V8. 4.4l are about as high as you can go (maybe 4.6l). And even then, the percentage of gain is lower than the displacement increase would suggest.
You have to make a choice: high revs with a flat-plane race engine like the S65 or arbitrary displacement (and thus, horsepower and torque) with a cross-plane like the S62.
It is not a coincidence that the M3 and the Ferraris use cross-plane engines. If you want torque, buy a C63 AMG.