How much does the modem speed have on the internet

im planning on getting a new router it is

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

and i was wandering that since it has gigabit ethernet ports would the modem bottleneck the speed of the conection i have the Embarq (ZyXEL) 660 Series modem and it only connects with 10/100. so if i hook up the router with gigabit ethernet ports. would i not get all of the performance of the router? or should i get a new modem that supports gigabit ethernet.