A D3 modem will bond multiple channels, IF bonding is available in your area, regardless of your tier. I believe performance is only 20/4 in areas with two way bonding, but it is possible to do it without.
Thanks to all for enlightening me. D3 modem is ordered! Will be burning in modem when it arrives and ordering service right after the first of the year. -- The difference between genius and stupidity is that genius has its limits.