Worf, for a 5.1 setup the surrounds should be on the side, rather than back, wall unless the listening position is right up against the back wall; in that case it makes little difference if they're on the side walls very close to the back wall or on the back wall spread out almost to the side walls. If the side wall position is used, they should be slightly farther back(maybe 2')from being directly to the side of the listening position, to give a little more "back" imaging in the absence of actual back speakers.
Incidentally, in a room that long there probably is going to be enough room behind the seats(say at least 4')to make a 7.1 setup worthwhile.
