For me the thing is this. I do not have matched speakers in my current setup but I once did for many years, 5 identical NHTs. Again back to my current setup, they are all of the same brand (Emotiva), they all use the same tweeters, and some even use the same mid bass/midrange drivers.
in my experience, talking front mains only, even with identical speakers there are small differences in sound based on their position in the room. I have heard it across several speaker sets. But only hear it when testing with pink noise. With music, I can't detect it at all.
With respect to the center channel, the differences between center and fronts become larger. Its easy to hear with pink noise. But I can't really detect it at all with music. The whole front soundstage appears seamless. Weather stereo or MCH. No different than I perceived with identical fronts/center.
When we get to the surrounds, the differences using pink noise get larger still, but with music things could get panned across the sides and sound the same. During the pan there was typically a hole in the middle side, but it also happened with the identical. I hear nothing that would point to a difference in timber.
The worst are the heights. There is a fairly big difference using pink noise. I think I could hear a difference in timber if given a chance to test it, but in actual use, for the typical stuff that shows up there, I'm not convinced it matters. It definitely doesn't matter for ambience or effects. It might for discrete instruments, but its very difficult to perceived it.
In short I think the physical location of the speaker, and probably our listening position in relation to it, plays a significant part in its timber, but it not like we can do a whole lot about it anyway.