So - I'm doing the first prep's for my new listening and entertainment room. Have tried out various loudspeakers and have decided to go for the BeoLab 4000s in the back, in spite of having BL5s in front. Yes, I know this flies in the face of those who'd like to have BL5s in the round, but I arrived at my decision by using my ears.
I took a number of films that I like, both action and more restrained films, and listened to their surround channels only.
First setting up with all speakers, ensuring that the weighting of the sound was correct, and then cutting out the front speakers. It's strange to only listen to the surround channels!
After having done so, I was confident that the BL4000s would do the job in the back. Have even tried with my BL3s, and for certain movies they may deliver an additional bit of helicopter clatter in the back (anything by Michael Bay) -- but the 4000s are more than adequate for my use. You'll be surprised at how low the volume is on the sound fed to the surround speakers.
There's one exception to this. I'm kind of mindful of my hearing, as I love listening to music, and I'm not keen on sitting inside rolling thunder for two hours.
I have friends who play their movies at levels that make the whiteboard sections in their walls separate with visible cracks as the subwoofers get into action (no joking) -- if that's the volume you want, then you want BL3s or BL9s in the back.
Movies: LOTR, Zodiac, Terminator 3, War of the Worlds, Being John Malkovich, Lost Highway, Back to the Future, King Kong, Eternal Sunshine of the Spotless Mind, Science of Sleep. (Gondry does some nifty work with subdued sound effects).