In the first paragraph you attempt to draw a conclusion about a difference in sound between amplifier classes.
Then in the next paragraph, you openly state that the comparisons were not conducted in a way that would allow you to draw any kind of conclusion.
So why even state the first paragraph, when you later openly admit that it is flawed?
It is kind of tough to compare different setups in different vehicles and keep things consistent

The one thing I have been looking for is a class d subwoofer amp that hits notes in the 30 to 45 Hz range with speed and precision, and thus far many of the systems I have heard just can't do it.
The differences you are hearing could very well be "real".....but you are incorrectly attributing to the class of the amplifier instead of the real cause of the difference (which is the result of known, measurable differences in things like power, gain structure, complete differences in setups, etc).
They are not, however, the result of the amplifier class.
I guess you didn't see my other thread where one of my installer friends invited me over to compare a Hifonics Brutus 1608D @ 2 ohms with a Lunar 2125 @ 2 ohms. The Lunar is rated to deliver 575 watts RMS at that load and the Hifonics topped out @ 800 watts RMS before major clipping occurred!
This test was conducted in a 2002 Tahoe, with a pair of phoenix gold 10" subwoofers in a properly ported enclosure off of a Pioneer DEH-800PRS HU and there was a clear difference on anything with speed and precision.
First, he played some DJ Unk... with the Lunar, then with the Hifonics. I was shrugging my shoulders saying I couldn't tell the difference. Other than the fact that I hate the new commercial rap garbage, the bass sounded the same to me with both amplifiers.
Next, he went back to the Lunar, and put in a Disturbed CD with some heavy double bass pumps. The Lunar hit every one of those double bass drum notes. On to the Hifonics, repeat the test... The double bass drum pumps just blended together and sounded like total ***.
Oddly, this has been consistent with 90% of the Class D subwoofer setups that I have heard over the past month. Rap bass or anything loose, no problem. Play something that requires speed and precision, and for some reason the Class D setups come up short. At first I was blaming it on the fact that many of the class d systems I heard were "budget" amps run @ 1 ohm. Next I blamed bass boost. It wasn't until I heard the Brutus versus the Lunar that I truly gained an appreciation for the difference since I was able to hear both amplifiers in the same vehicle.
Oddly, this all started out with asking my friend how the Hifonics XXV series was because I wanted to put a Colossus on my pair of dd1508s in my Civic. He said, and I quote "Class D is garbage" which is not something I expected from a 20 year old MECP certified installer. Then he invited me over to hear the difference in another friend's Tahoe that was at their shop. Sure, the PG 10s may not be the best BUT there has to be a reason why the Lunar performed WAY better than the Hifonics on those double bass drum pumps with the only difference being a change in amplifiers. In this case, maybe it is strictly budget amp versus quality amp....