Sometimes I will leave the lid closed on the first pizza if it still has not reached my ideal temperatures (750) or so. If I have a very lightly dressed pizza I would rather be 800+ degrees. I have never attained the 900+ range with my Genesis and have given up that quest for now.
With the hood partially open you get a better convection, or so it seems. Hard to tell since I have no way to actually see the air flow.
Experimenting with it is the fun part, give it a few trials each way and see what works for you. Eat the failures or share it with the dog if you have one. My dog looks forward to pizza night, although the failures are rare at this point. Once you get the hang of it, you should be a pro.