Multiple Subnets on the Outside Interface of a Cisco ASA

Recently I had a customer provide a Cisco 2821 router along with a Cisco ASA 5520 to setup at a DR site.  The router was provided in case the ISP provided a small subnet for connecting the router to the ISP's equipment (usually a /29 or /30), and also gave another subnet that would provide the functional IP space for the customer's equipment (something like a /24).

This network in blue has been a reoccurring pattern over the last few years and I want to put forward the simple premise: Use the ASA by itself instead of putting a slow router in front of it.  Let me be clear there are perfect reasons to have a router in front, such as if you are running BGP to route the subnet you have, or to have another layer of control.  My point here is don't put a slow router in front of a faster firewall and don't start asking your boss to buy an expensive fast router just to add another hop...