I've found that 5.1 provides a better surround effect than 7.1. I have a similar setup to yours (TV in corner) and it's not bad, as ppl make it sound. I've experimented with different 7.1 vs 5.1 setups, and ended up using 5.1 with fronts and surrounds forming an "X," or a square around me at 90 degree angles. This creates a a great sense of envelopment untouchable by any 7.1 setup I've heard. 7.1 pulls the "surround stage" (my made-up term vs. soundstage) heavily to the front, with support information from the sides, and almost nothing from the rear. Most soundtracks are still 5.1, and although 7.1 soundtracks are growing in number, I've rarely heard more than a relative whisper coming from those rear surround channels.
My $0.02 is to go with 5.1, strive for 90 degree placement and then play with time delays if your receiver/processor allows. Which reminds me, I'll need to change my signature someday.
Pioneer | Cambridge Audio | Dynaudio | Identical + equidistant 5.0 | KISS