I need to buy a modem and was thinking of buying a Motorola Surfboard SBG6580 but i was reading reviews that said gateways (modem with built in router) actually sacrifice some speed compared to regular modems. The Motorola SB6121 seems to get the best reviews but it max output tops out at 160 which isn't as fast as the SBG6580. And in 2-3 years wont be able to keep up. If I did by just a modem I plan on purchasing a new Airport Express. Any Thoughts? F.Y.I. Cox is my ISP.