I'm not sure what you're really asking, but i would say this.
An antivirus with the windows firewall is more than good enough for most folks. Also modern systems don't suffer from a performance penalty with such programs installed. With the amount of processing power and ram we have it's just a non issue.
It's also good practice to have a NAT router between the internal network and the modem. This will then deflect any packets which do not have a destination in the internal network.
When you refer to the speed of the router i'm not sure what you're getting at, but any modern router will be fast enough for most consumer internet plans with the only exception being people with a fiber optic connection running overwireless where they might not get their full bandwidth through the wireless connection.