" I really like the XA 5; haven't tried the XA 6. "
Been wearing the XA Comp series for years. Just got a pair of the XA Comp 6 and took them on a hike in June. If anything they seem even narrower than the 5 - got some blisters in places that I've not had them before (outside of my foot, outside edge of both big toes.) But I was wearing a different model of sock, too, which may have changed the fit (though they don't seem thicker than the old socks in hand.) Got a fairly stiff superfeet-style insole during a town stop and that helped, but by then the damage was done. Not sure what I'm going to do now.