The only way that a router would slow down your connection is if that it could not handle your conenction coming in. This only happens with some of the lower class routers. Brands like D-Link, Linksys, Netgear, and SMC will work fine. Also, adding another IP will not necessarly add bandwidth because it depends on other factors such as other people using their cable connections at the same time and the overall traffic congestion on the Internet