Well, you're not really "switching IPs" so much as you're doing failover redundancy in your network. This can be accomplished with some expensive business routing equipment ($10,000 Cisco Business routers and the like) but not with home equipment to my knowledge. If this is for a business then you'll need to hire a consultant to do that analysis for you. There are simply too many things to take into account to answer properly here in a forum when discussing business failover clustering. Things such as link speed, network re-convergence, network topology, etc are all factors that come into play when considering this sort of setup.