7.1 speaker placement

1000 pardons if this has been covered, I could not find it in a search.

My room setup will not permit me to have the primary sitting area anywhere but against the back wall. This means that to add 6th and 7th channel speakers, they would have to either be mounted on the back wall above facing forward, on the back wall angled down, or in the ceiling pointing down.

I currently have B&W DS7's for surrounds and ideally would use the same for rears- so I have the option of configuring them as mono or di-pole.

Anyone with this room issue gone with 7.1 and how effective was it given that the rears are not behind you?

Thanks for the thought out responses. I think staying with my 5.1 setup makes the most sense all things considered. It seems unlikely that I will see any tangible benefit versus the $ expended on two more speakers and amp channels.
There's no substitute for evenly spaced speakers at ear level and a minimum of room correction. Even with my smallish home theater space, I would never go back to 5.1.

In my experience the key to decent 7.1 is matching speakers (no dipole surrounds) and not depending completely on automatic room correction. I'm not a professional installer but I've have set up a few systems for family and friends with very satisfactory results.

The most difficult was a listening position against the wall. LCR on the same plane and as close as possible to the display, The sides on stands directly to the side of the listening position and the rears mounted high in the ceilings corners aimed down at the listening position.

After the subs EQ program I ran the correction using the distance, volume, and the bass management. Manually adjusted out the EQ down to 200 Hz to taste.

Next comes fine tuning using my favorite surround queues from Master Commander (a 7.1 must).