One of the many ways to speed up your WAN can be to tweak your Maximum Ports if you use DD-WRT.
While paying for 20 meg, after an update, I dropped to 2.6 mbps. Upon investigating, all of my settings were the same except that the Maximum Ports had increased to 2048. The older router has very little ram, so I slowly decreased the amount until the magical number of 1024 was established.
By decreasing my Maximum Ports to 1024 on an older Netgear router, my download increased by 17 mbps. (Average user)
Decreasing this number can prevent router slowdowns also.
This will depend on the amount of memory your router has and if you use QoS or P2P.
This setting is found under Administration in DD-WRT at the bottom of the page.