Okay, so being neurotic, I ended up ordering the Rossi in a 7.5 (in addition to the 8.5) and the Langes in both sizes. I'm glad I did. (I have a fedex discount through work.)
At this point, I'm leaning towards the Rossi in a 7.5. It really locks down my heel, which is great, but it does it less painfully than the Lange in the same size. With the Lange I feel the plastic bearing down a few places around the heel, keeping it in place. It's not too painful, but it's nice not to have that feeling with these.
The issue I have with the 7.5s is that even with the buckles loose, the boots feel uncomfortably tight--I feel a throbbing sometimes (like you feel when a bp cuff is on, but not at its tightest). This happens in the left (larger foot) and the right.
I have a couple other issues on the left: I feel my big toe ramming into the front of the boot. Weirdly, that didn't happen with the Lange. I thought that maybe the Lange liner has more stretchy material around the toe, but I notice that I feel it in the Rossis if I kick something while in the boot. This was a worse issue with my last boots (the Tecnicas). In fact, with the Tecnicas, before getting that fixed, my toe became tender enough that skiing crud or bumps was painful. My sixth toe is also feeling cramped.
Both of these issues can be solved with grinds or punches, I realize. What about the throbbing? Is this boot just too small? Can I expect it to pack out and alleviate the issue? I also notice it with the Langes in a 7.5 with buckles loose. I got frostbite on the end of my left big toe in December, so I'd like to keep the circulation going so I don't repeat that.
I should note that I'm using custom footbeds, (Amfit, based on weighted foot shape).