Everything started to work 2-modem replacements later since the units he had along were swapped-out versions during the day or whatever was left in the pile before driving out in the morning. Of course, last night I decided that it would be better to keep the systems together and so transferred the modem back into the office.
The new SMC modem is DOCSIS 3 compliant and has 4-ports gigabit speed. That fact became more obvious when the FVS336G speed led lit up green (1000 Mbps) instead of amber (100 Mbps).
In terms of the feature interface, no changes at all apart from the fact that Full Speed 1000 Mbps is now available. Hmm, time to call Comcast Biz and get the other modem router replaced! Why? Well, see the speed test on that one under no load :-/