The rated absorption value (a laboratory measurement related to the capacity of a flour to absorb water) for the King Arthur all-purpose flour (KAAP) is around 60-61%. Using measures such as sifting the flour, using autolyse or similar rest periods, and using a whisk as part of the mixing process, I have been able to squeeze enough water into that flour to reach a hydration of around 65%. That value is a close to the "operational" absorption value for the KAAP (see http://www.pizzamaking.com/forum/index.php/topic,4646.msg39204.html#msg39204
) and is also comparable to what the old NYC masters used to make their NY style pizza doughs before all-purpose flour was replaced by bread flour and high-gluten flour. As a practical matter, I don't see much reason to get above 65% hydration for the KAAP, although I might try a percent or so higher to make a dough like JerryMac's as originally given at http://www.pizzamaking.com/forum/index.php/topic,5851.0.html
and as I interpreted and modified his recipe at http://www.pizzamaking.com/forum/index.php/topic,6515.0.html
I will also acknowledge that there are dough recipes out there that call for very high hydration values. Peter Reinhart and Jim Lahey and others are proponents of very high hydration doughs, with some examples being given at http://www.pizzamaking.com/forum/index.php/topic,203.msg54497.html#msg54497
(Reply 19), http://www.pizzamaking.com/forum/index.php/topic,7745.msg69521.html#msg69521
(Reply 31), http://www.pizzamaking.com/forum/index.php/topic,8148.msg70104/topicseen.html#msg70104
(Reply 3), and http://hollosyt.googlepages.com/quickrusticciabattapizza
. One member even mentioned that one of Jim Lahey's no-knead doughs has a hydration in excess of 100%. In my opinion, recipes such as the ones referenced above work much better in a very high temperature oven than in a standard home oven such as yours (and mine). I just don't think there is enough heat in a standard home oven to give the oomph that is needed to raise the very wet doughs to optimize the results (good oven spring, soft crust and crumb, and everything properly baked). I have also found that the leftover slices of such pizzas when baked in my home oven do not dry out enough on reheating. They invariably remain soft and soggy even after a long reheat time in my toaster oven. So, when baked in a standard home oven I think it is best to eat these types of pizzas right out of the oven with no leftovers. As I also mentioned in Reply 31 above, in addition to obvious handling issues, there are some limitations to high-hydration doughs in terms of the amounts and types of toppings that can be used and the sizes of pizzas that can be made with such doughs. These limitations do not exist with normal hydration levels.
There are also other issues that complicate the hydration of doughs. These include humidity, flour moisture (which diminishes from the time that the flour leaves the miller), flour age, storage conditions, and even variations in the type and quality of protein. Even when weighing the flour, it may be necessary to make adjustments to the flour and water in the mixer bowl to compensate for these factors. This is where getting to know the right "feel" of the dough is so important.
The presence of oil in the dough will also affect the rheology and plasticity of the dough. At low levels, it is not likely to have a great effect. But, at high levels, for example, above 7%, the oil can affect the overall "hydration" of the dough because of the wetness of the oil. Having made many doughs using high levels of oil, I found that I had to reduce the nominal hydration of the dough (due to the water) in inverse proportion to the amount of oil used. For example, when I used 7% oil, I used a hydration of around 56-57%.