Thanks Guys.
Just swapped out my modem, now on the CGN3.
It came pre-loaded with 4.1.4.5 - so I guess I have to wait for the upgrade to come down.
I called Rogers tech support, and they have a record of the CGN3 performance issues in their internal bulliten system, and said the approach on their end to resolve is to send a maintenance ticket to the correct department for a 48 hour turnaround time to resolve the issue. I assume this means that they will push the updated firmware down to my modem as a result of the maintenance ticket.
Will post back once my modem is upgraded to 4.2.4.3.