Great thread lots of good info here!
Just waiting on my son to turn 1 and both our kids will no longer need the rear facing stuff, whew!
I plan to throw the Recaro Pro Ride in the M3 for sure. We also have a Diono Radian folding unit which is really small and a Maxi Cosi which is a bit larger but has a cup holder. Those latter two I don't plan to use in the M3 - those are better fit for SUV's and larger cars.