Thanks for the comparison comments! Very cool to be able to evaluate these two cars back to back. I'm not surprised to hear that a wagon can be well balanced, particularly one with the pedigree of the E63!
I'll be interested to hear which settings on the BMW most closely match your preference on the E63. There's something to be said for simpler, although flexibility may end up enabling you to cover a broader range of applications with the M5. As you wrote, it may take time to figure out how to best configure the M car.
I'll try to keep my questions under control, but....
Regarding seats, do you have the width adjustable seat in the M5?
Does one or the other feel stronger - more eager to go?
How does the E63 like being pushed harder, closer to the cornering limits, in rapid transitions?
Cheers, and thanks for describing your experience.