It seems like it would be about things like a large turkey, a tagine, beer can chicken, other taller things one may imagine.
Specifically addressing your items: I have the standard height 950 FGM, and I don't know if the extra 3" will give you enough height to make a significant difference for anything you just mentioned. Maybe beer can chicken, I'm not real familiar with that. A large turkey in a pan is taller than 12.8" in my experience and getting it through the door would definitely be a challenge, width-wise as well as height - and then managing it while it cooks will be tricky. What's the width on the door on the smaller oven that you're looking at? Because you'd need to get the turkey in roasting pan in through the door, and the door is going to be narrower as well as shorter than the inside of the oven. And I guess it would depend on the tagine but I think you'd be tight even in the taller oven. The two I just looked at on Amazon, you could probably fit the Emile Henry tagine but I'm not sure about the Le Creuset one.
By the same token, I'm not sure you're sacrificing that much for Neapolitan pizza if you go with the taller oven. I haven't cooked in the taller FGM but I have cooked in an Italian oven with a much higher ceiling and bigger opening than the FGM and it cooked beautifully. It's a management issue more than a good/bad issue for a household oven, IMHO. You're not putting in a restaurant oven that has to perform at maximum efficiency for a multitude of users, you can spend a little more time managing it if you need to, and you'll learn your own oven and how best to cook in it, and that trade-off for the versatility of the taller oven may be justified for you. When we bought ours, we didn't have the taller option available so it was an easy decision. If we had had to choose, I'm not sure we wouldn't have opted for the taller oven. It would be nice to have, and my 950 is so efficient, I can't imagine loosing that much with the taller/bigger opening.
I haven't gone back through this thread - have you looked at either actual oven in person? I think that would really help, it's very hard to imagine the size without seeing it in reality.