I wish people would stop quoting it - it is a totally pointless and meaningless measurement. The saddle could be any width, almost. And you must try it before you buy it and have the fit checked, surely?
i would have said 7 inches was a narrow fit, my lass' saddle is 9 inches between the d rings and is classed as being medium wide fitting, but please please get it checked by a saddler to fit your horse as saddles vary in size between makes much like a pair of jeans would.