At only 14 ft wide I would suggest only 6.1 as there isn't much room for the extra channel to spread out the sound any more than 1 speaker would. I am running 6.1 and noticed quite a difference from 5.1. You could always experiment with a 6.1 and 7.1 setup before finalizing and see which you like best. Borrow some speakers if need be to do the testing.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70