I don't have any numbers, but when I last took my S75 in for service I was given a S100D loaner. I drove the loaner to work and immediately called the service center back to have them check that everything is working correctly with my regen, because the regen on the 100D was VERY noticably stronger feeling. My regen was working properly, and the difference was just the second motor.
My wife's old 2012 S85's regen started earlier and seemed stronger (at least at first, it may not have been at peak) than the regen in my 2015 S P90DL. I noticed it every time I drove her car. And I was always surprised as I expected more regen in the D.
The regen in her new X 100D must be closer to my car's, as I have not noticed it.
Acceleration and regen both feel completely different in the older RWD S vs the dual motor S. While max regen values in kW are, essentially, the same between the two configurations, the regen onset and ramp feels much more aggressive in the dual motor cars. Similarly, the D cars (even the slower ones) accelerate with a hard initial jolt that tapers off, whereas acceleration feels like a more gradual surge in the RWD cars.
I recently drove a Model 3 and the sensation of acceleration and regen reminded me a lot of the old RWD S... which left me wondering: will the dual motor Model 3 feel more like the dual motor Model S in this regard, or will it also feel like the old RWD S?
Ok, that makes sense. The faster onset would tend to cause more rotation throwing more weight onto the wheels, and off the rear ones. Not an issue when you can regen off the front, too, but with RWD you'd want to have a slower onset to keep more weight biased to keep traction back there. So you end with the same regen kW but a slower build-up to it.