Re: Will 7.1 sound good?
Definitely do not go for the 7.1 setup. You will regret it in the space that you have describe. Not to mention, there is barely a handful of true 7.1 mixes out there. So all you are getting is an extrapolated extra couple channels, blurring the spatial distinction between your rear L and rear R.
A couple other notes about the setup you have described. A dead room is not always the based. This is a matter of debate among acousticians, but I am a believer that a truly dead room takes the life and warmth out of the sound. EQ can do wonders but you are still starting with a dead room.
You say that you have a pretty dead room but I don't see how that is possible with the amount of glass that your have in that space. Glass has a fairly low absorption coefficient, as does most concrete. So basically your reflective rate with the materials in your room should be really high. You need carpet on that concrete, drapes on the walls, and fiberglass has nice high absorption coefficient.
And finally, you said you have the surround speakers to the sides, aligned at the front of couch at ear level. If you are listening to true 5.1 mixes, this may present a problem as you have no surround speakers behind you. I, personally, would not put the couch all the way against the wall and place the rear speakers behind you. And make sure you get yourself a good subwoofer to fill in your space.
In the end though, with the materials in your room, and the speakers that you have, I would say that a good EQ Room Calibration is in order.