The traditional solution to this problem is to sell a fractional circuit with bursting and average billing for overage to let the economics work things out. It

The traditional solution to this problem is to sell a fractional circuit with bursting and average billing for overage to let the economics work things out. It actually is quite a bit harder to run a network _well_ at 80% than at, say, 60% because you have to deal with reboots/etc. in your network as well as routing issues if your peering changes and the excess capacity hides a world of sins. Lots of issues.