If you are not seeing any issues with your current router, and you are not on the 105 Mb speed tier, then there is probably no reason to upgrade your router. The router and modem will negotiate the correct link speed between them.
Thanks for that information, you provided answers that I have not seen in other posts.
Next question? Now I have this Gigabit modem connected to my aging PC through my WRT160N router, the bandwidth is still 100M, so why do website seem to use more of my 2G RAM than before installing the Gigabit modem?