Well the real question is, do you notice speed slowdown's during peak usage hours(7pm-11pm/1am)? If so a newer D3 modem would benefit you, as your using a D2 modem. That is limited to one downstream channel, and one upstream channel. That one downstream channel has a max bandwidth of 38mbps, and its shared locally with others on your node.
With a D3 modem you can bond up to 4 downstream channels, and 4 upstream. There are even newer D3 modems that can bond up to 8 downstream channels, and 4 upstream channels. So simply with a D3 modem you will have more bandwidth available to you, so there are a lot less chances of speed slowdown's during peak usage hours. So your connection would be even more reliable with a D3 modem. However D3 modem doesn't mean you will get faster speeds then you pay for, you will see faster short burst of powerboost speed, that last a very short time though.