If I currently get an average of 20mbps using a linksys n router with comcast as my ISP. If I upgrade to an ac router, and assuming I have ac compatible devices, will I get any significant increase in wifi speed? I wasn't sure if I need to get a faster internet tier from Comcast or not. AC routers promise much faster speeds (400mbps) but comcast says they provide me with 25 tops. Can I just upgrade my router or do I have to pay more to comcast?