By the time I had the opportunity to fly a D model I already had 4 years of flying Betty Jane under my belt. I was really used to the B/C. I've sat in countless D models over the years and bought backseat rides in 13 of them prior to us getting Betty Jane. But, never flew a D from the front seat until 2013. The cockpits feel completely different. The B is more reclined and there is a lot more distance between the panel and the seat. The trims are easily accessible with the T-6/early Ball type throttle quadrant. The canopy is restricted in a couple ways. It takes a while to get used to the birdcage, but after a while you don't even notice it. You can't open it in flight, and if you open it on the ground with the engine running you are putting your life in the hands of the crew chief when it blows off the airframe

. I never tried opening the side sliders in flight, it didn't really matter, it was hot no matter what was going on. Flying, it is a tad faster than a D at the same manifold pressure in cruise, and that can probably vary per airframe. I found that landing the B/C took a couple extra miles an hour over the D. I don't know if that was due to the extra weight of the turtledeck and/or the extra weight of the rear cockpit? It will still 3 point beautifully, just a tad faster. It really drops out of the sky if you get it below 110 on short final, but once you transition in to ground effect it's a pussycat and slows right down.
Getting in the D the first thing I noticed was how close the panel and front cockpit windscreen were positioned. The other thing is the massive throttle grip jutting out from the left longeron. The entire quadrant is deep enough that it makes getting to the Rudder and Elevator trims awkward. After a about 15-20 minutes you get used to it, it is just different. The D seat feels, to me anyway, a bit more upright and not nearly as reclined as the B/C. Landing the D is night and day over the B/C, you can actually see where you are going and it rounds out to a tail low touchdown with almost no effort.
Flying and acro feel the same, speeds are the same, power settings are the same...they both fly on rails, nothing else like it.
John T is correct about the wings. Chris Fahey at POF took a ruler to the A,B, and D...there are some minor differences in the doors but overall the ammo bays are he same. Also, we had some damage to our right flap a few years ago. I ferried the airplane (with a permit) to FL for repairs. American Aero hung one of Toulouse Nuts flaps on to get us through the season...so the parts are interchangable. Hope this is informative.
Jim