There's so much talk about strictly matching the front three (with which I would agree in principle), but how many people bother to or even can have the center tweeter at the same height as the tweeters in the front mains? Somebody recently posted about whether it would matter if his center was four feet lower while the left and right were like five feet closer to the seating area! Might as well not sweat matching in that setup
Unless you are really anal about speaker placement--have calculated room modes, measured to the inch on the exact angle . . . you're not going to hear the difference. Some with real technical knowledge argue the head related transfer function obviates the need to match the surrounds. So, I wouuldn't sweat it.
UNLESS, that is, you're talking about drastic mismatches like electrostatics with conventional woofers or horns, etc.