Did I read your post correctly that the WF on Elcamino in Mt. View carries Grande by the loaf? Did you get over to the GM yet?
If I locate a loaf, what has more stretch, the whole milk or the part skim?
Yup, I walked out of WF on El Camino with a 7# loaf of whole milk Grande on Saturday! They didn't have it in the display case but had individually chunks. I scooped up all that I could get when one of their employees noticed and said "Man, you like cheese!".
I mentioned that if they had a whole loaf, I'd buy it. She popped into the back storage room, returned a few minutes later, the loaf was on the scale and in my greedy little hands shortly thereafter. I haven't used it on a pizza yet but made calzones last night. It's funny to cut into a calzone, watch the cheese oooze out and see how far you have to stretch it to get it to cut loose so you can eat it!
Haven't made it to GM yet! I did try to get to the Cheesesteak shop but children-interruptus nixed that deal.
As for stretchability, I have two novice comments so take them FWIW.
First off, I always buy the block/loaf of cheese. I do this because although the pre shredded stuff is more convenient, I think the shred-it-yourself path makes for more stretchable final product. I determined this empirically but now think it has something to do with the anti-clumping stuff they put on the pre-shredded cheese.
Second, I'm sort of in an odd situation as my wife won't eat just about any cheese except mozz. So, I end up making just about all my pizzas with only whole milk mozz (shredded from a loaf). I found that when I do slip in a mix of cheese, the stretchability is reduced.