The surrounds are less critical, particularly for movies.
Right.
If you're going to use those Rear Surrounds for all-channel music, you may want some timbre matching. But for movies/TV, I don't think it matters at all. In fact, regarding the rear surrounds, I think very little matters.
The only thing you're going to get from those speakers is an occasional sound effect. Maybe the background hum of a crowd, or the closing of a door, or a creak in the floorboard, or a phone ring, or a doorbell, etc. There is so little from the rear surrounds that many audiophiles stick with 5.1. Also, there is really quite a small selection of 7.1 material out there. A few blurays. So most stuff that comes from those speakers is artificially created in your AVR from a 5.1 source.
I've had very cheap speakers for rear surrounds, and currently have $1k/each towers back there, (simply because I kept replacing my fronts and moving the old speakers back). If I was starting over, I would focus spending on the 3 front speakers and subs. I'd spend less on the side surrounds, and much less on the rear surrounds.