The knock on clipping biner to biner is that in some orientations, it's easy to twist one and get it to pop out of the other. Two locking biners clipped together is pretty bomber.
Regarding the op: Back when we were all climbing on 1" webbing, girth hitching runners was no issue. As the bdel data indicates, however, as one or both slings become thinner, the joint becomes progressively weaker. Personally, I would do it in a pinch, but I wouldn't make a habit of it.