I don't know about going bigger than a large, but one thing is clear to me:
Never order a small or medium pizza.
Smaller pizzas suffer from the wrong crust to non-crust ratio. Additionally, they often end up too thick/bread-y and without any crisp crunch.
IMHO, the correct size for a pizza is the standard large, i.e, the size of the standard pizza box size.*
And yes, quantity ≠ quality. (Remember Pizza Hut's "Bigfoot"?)
*Does not apply to artisanal pizzas, which are a different beast altogether.