How would they relay that information to the viewer, though? You either have to trust their opinion on it or hope that what they show you on screen is an accurate representation of what you would see in person....which it probably isn't going to be.
Digital Foundry is the source everyone usually goes to for this, and even then you have to trust what they're saying. People sometimes have different experiences because the "quality of upscaling" is completely subjective. What FPS people get with what hardware and other pc specs is not (or at least is a lot less subjective, someone's PC can be more or less out of whack and give somewhat different results).
The size of an extended cab is objective information. You can even come up with metrics of measurement to make it easier for people to visualize what they can fit (how many luggages of X size, for instance).
*Edit* I guess if you went above and beyond to get some truly average people to do the test, or just get some guys the majority of people trust that could be an okay-ish way.