DOCSIS 3 modem and N router
Beings you are on the Comcast 20/5 it would pay you to get a D3 modem. If you are in a D3 area that will give you 4 bonded channels down. If your not now in a D3 area, you will be before long.
Your speeds will be more constant with the bonded channels. No more of the 6 to midnight slowdowns.
They are also testing bonded channels on the upload so that will just be a matter of time.
I use a Motorola SB 6120 modem and a Netgear WNR 3500L router and that setup works excellent doing the same thing you want to do.
Bestbuy carries both the modem and router.