For me it would depend on how far your sofa is off viewing wall.
If you follow the rule of thirds for standing waves, your sofa should be about 12' off the front wall. This puts your surrounds at 12.5-14 from front and only leaves 4-6 feet of breathing room for your rears. Not ideal.
Too small to take advantage of 7.1 imo.... rears will smear into surrounds and become indistinguishable. Soundfield collapses.
Wouldn't consider at less than 20+ feet or so.
+1 for putting saved dough into good center channel!