DOCSIS 3 channel bonding allows for reaching higher bandwidth than the standard available 38Mbit/s downstream and 27 Mbit/s upstream per channel. ISPs commonly use nodes capable of bonding 16, even 32 channels, which raises some question as to the compatibility, and capability of older cable modem models.
DOCSIS 3 modems are commonly capable of bonding 4, 8, 16 or even 32 downstream channels. However, with lower cable tiers, the older 4x4 (4 downstream and 4 upstream channels) modems are quite capable of delivering the same performance as the newest expensive models.
4x4 modems are capable of delivering up to 152 Mbit/s downstream, and 108 Mbit/s upstream after overhead, theoretically. Their only other limitation is resource utilization, i.e. older modems may have lower frequency processor, more limiting chipset and less RAM.
If using a lower tier cable service you are generally safe with speeds of up to 50-60% of the theoretical bandwidth capability of the modem. In such cases there is rarely any benefit in upgrading modems to the latest and greatest. The only exception is, if you are getting slowdowns at peak times, a modem with more bonded channels may offer a bit better consistency through its redundant channels.
Note: EuroDOCSIS uses wider 8MHz downstream channels, capable of ~50 Mbit/s per downstream channel.
Also see:
What is DOCSIS 3 channel bonding?
