I fully plan to create some "optimal" exposures, that was actually the entire point of renting the A7r in the first place. It also so happens that this weekend is the last weekend for fall colors in the mountains. It might be raining, not sure yet, but I'm going to try to get some landscape photos, every scene with both cameras, bracketed, etc. I don't have a lot of time to go hunting for awesome landscape scenes, so don't expect any kind of impressive artwork, but I always planned to do a more rigorous comparison between the two.
I've seen lengthy geometric proofs for the fact that a square is the largest rectangle that can be inscribed in a circle, and even lengthier algebraic proofs that 1 + 1 = 2. At the end of your testing, I'd be quite surprised if don't conclude that the a7R has more DR than the 5DIII and you can push the shadows harder.
Still, there's value in demonstrating to ourselves that which we expect to be true. Enjoy!