Why is my router limiting the speed of connection?

I have run into these problems once before, it turns out many routers just are not prepared for that kind of speed on the WAN side. weather it is cpu speed or not I was never sure. could have been the switch ports for all I know but we fixed it with a new more powerful router. We simply researched specs on routers until we found one that looked like it met the requirements. I don't like to recommend certain brands but there are routers out there that are up to the task.