I think everyone that posted so far is correct in some way and touches upon all the main aspects of the topic.
I can certainly feel what ElAurens says, but that's through years of perception under controlled conditions (same control profiles, peripherals, software used, etc): in the previous IL2 series it didn't feel the same doing 500km/h in a 109 and doing the same in a 190, but it took quite some time to notice it.
In a similar fashion, when i first took up a 111 in CoD it felt much heavier and full of inertia than whatever bomber i had ever tried in IL2, but in a way that didn't feel uncanny. To the contrary, it felt just right and i had the feeling that the extra weight and size really showed.
I think the variables are too many and while it's true that i can't think of something that can't be quantified and measured (like Doggle says), maybe we don't have the technology to take advantage of it yet. Of course it's mostly fundamental newtonian mechanics at the speeds and masses we are talking about, but how many consecutive higher order derivatives of a certain function can a current PC compute per second and at how many instances and points across the aircraft's surface before melting?
It's also difficult to quantify objectively because of the same reasons: few or no surviving aircraft, probably different in handling than when they came off the line after all these years (refurbishments, weight changes due to modern avionics installed per ATC rules, removal of guns, etc), a dwindling amount of veterans who all have their subjective opinion (depending on their flying habits) and a multitude of sim fliers with millions of combinations of different controllers and input curves.
It's a nightmare
I think that technology-wise Xplane is probably the closest one can get to having a wind tunnel emulator running on a PC (as long as the individual flyable is also done to a high standard to take advantage of the sim's engine in full), but sadly it will be some time before we see such technology in combat sims: it's so taxing that with full multi-core support in Xplane 10, a current PC can not run more than 4-6 AI aircraft with the same FM accuracy at the same time without noticeable performance loss. In fact, there are people who take Xplane flyables, simplify their FMs and reissue them as AI-only aircraft to populate the game world.
P.S. Very interesting topic
