So we recently upgraded from dsl to cable internet to get a bump in speeds. When I test the internet speed with one computer hooked up directly to the modem, it easily breezes to 50 Mbps down, but when I plug in our old router (an SMC Barricade SMC 7004ABR) and the speed drops to 5 Mbps, at best.
I'm looking for suggestions for a new router that I can drop in and which won't limit our internet.
Here's the current wiring diagram.

The wireless router is a linksys WRT 360N is used as an access point on the 2nd floor since all the other networking equipment is in the basement.