The problem is that the image-rotation routine in WC assumes square pixels for its calculations, though. If a spacecraft or other rotatable object in view at a fixed distance is rotated from a horizontal towards a vertical orientation, it gets noticably longer and thinner with non-square pixels, pretty much the same distortion effect that you get with 4:3 material stretched to 16:9 (what I also dislike, btw., for that very reason), just rotated by 90 degrees.
I'll have to verify that at some point, but you may be correct about how rotation was done. (Sigh... yet another thing for me to look at.) I did some investigating with the raw image resources. In some places, it's very clear that stretching to 4:3 is the right thing to do.
Here's the planet from the victory sequence:
Here it is again, stretched appropriately for 8:5 -> 4:3 conversion (pixels 6/5 higher than wide):
Just in case it's not very obvious which one is more circular, I've drawn circles around them using Paint.NET's ellipse tool (holding shift to force a perfect circle):
Clearly, the stretched version is better.
Here's another example, this one from PLANETS.VGA:
...and with the same circular highlights:
Problem solved, debate over!
...Right?
...Except for these, also from PLANETS.VGA (uploading only the highlighted versions because of image limits in posts):
(The sun has a blue highlight because the red one was too difficult to see. At this size and against this background, the blue isn't much better. Sorry.)
So it looks like some of the resources were created with stretching in mind, and others weren't. That makes it a little more difficult to decide on a "correct" answer.
My conclusion:
There are inconsistencies in the in-flight artwork, but all of the surrounding stuff (the cockpits, the sequences between missions) all look much better (to me) at 4:3 than 8:5. Monitors of the time were all 4:3. Players at the time (almost always) played at 4:3. 4:3 is therefore still the best default ratio, although there is some inconsistency in spaceflight.
But I will ask Denis as you suggested and take his oppinion as the final word on this. I wanted to ask him something about the Scimitar's cockpit anyway.
I'm looking forward to his response!