I have never gone by the "percentage" rule with cables. I think that an expensive cable is worth it when it's the cheapest way to improve your system. IMO, a box or speaker upgrade should sonically exceed the sonic contribution of a cable upgrade. But when your system becomes expensive to the point where better cables offer a significant sonic upgrade for much less then a black box upgrade, cables are the way to go. Cables are the icing on the cake, but you need to have the cake first.
