Here's a fun thing.
If you do go and have 2 x circuits - and have 2 x HG612's - I found whenever I configured LAN2 to both be on my LAN, i.e. so I could collect stats from both modems - strange things would happen on the LAN and traffic would just fall through the floor for everyone.
As soon as I disconnected a LAN2 for one of the modems, everything returned to normal.