How important for surrounds to match fronts?

My opinion, if you want to achieve the movie experience like/better than the theatres in your home in a medium to large space to work with, you will need horns and the less crossover and calibration the better as it is all filtering holding back dynamics and natural quality. If speakers are chosen correctly, crossovers and calibration will be minimal. Identical speakers/drivers are best for timber matching across the range. Dipole speakers beside or behind listening position or both are beneficial to surround duty. Carpet or cork is good for flooring and paneling behind front speakers on wall and in back corners work extremely well. A suitable sub(s) are the icing on the system for low bass duties. Placement is critical with sub(s) as to smoothen out the low end. In the end if this achieved, everyone will come to your house for movies instead of paying and waiting at the local theatre. Enjoy and cheers!!

Not important

not real important. The center is the most important for 7.1 with the r/l being second. Surrounds are nice to have similar but the amount of sound coming from them is so small compared to the fronts. Dont cheap on the center or go Phantom on the R/L and dont sweat the surrounds.

We sit pretty close to the apex of an equilateral triangle with the front LR speakers. I removed the center channel because the mains (KEF 107/2s) image so well dialog is intelligible and seems to follow the speaker. Placing a matching speaker in the center of a projection screen would be impractical and is unnecessary.

Rmichael21, I'm not sure if you are still interested in answers, but in the event that you are, I'll add mine.

I think the answer to your question depends on the value you place on your HT experience. The more value (and means) you place on your HT experience, the more likely you are to value the timbre matching in the surrounds.

My interest in HT is mostly casual; I like it but any extra funds I have usually go into my 2 channel system. My surrounds are not timbre matching and I'm good with that.

Having said this, a recent experience is causing me to rethink the need for timbre matching surrounds. Earlier this spring, I caught the bug and decided to "upgrade" my L/R mains; but, I decided to keep my existing center channel. While I'm quite pleased with the stereo sound in my new speakers, the surround sound experience can be frustrating at times. The only reason I know this is because I used to have timbre matched speakers across the front. Now I'm wondering what my experience would be like if I was accustomed to five timbre matched speakers instead of three.