Any of the new plans you would have had to move from the smc. It's only a 4 channel modem and quite possibly would start noticing congestion issues with it as time goes on.
For the 60 plan you can still now use the 8 channel ones. The cgn2 and the cisco.
One hing to check on your current. What wireless are you connecting to? The 2.4 or the 5? The 5 which often will have less interfearance, does have a shorter range. Interfearance as a whole might be an issue if you are on a different channel than before.