Cable service and modem compatibility

Hah, well I think they can get away with the CM1000 claims for now since I don't think I've ever even heard of anything close to a 6 Gbps option for any ISP!  

Unfortunately it seems that Xfinity not only recommends 600+ Mbps modems for this 300 Mbps service, it seems they require it. They were unable to load the appropriate boot file onto the CM400, so even if I lived in a place where I was the only customer on a node, it doesn't seem like I could use this modem. The support ticket was escalated several times without success (and without response from Xfinity for long periods of time, but that's another story).

In my case, I don't need 300 Mbps, but it was actually cheaper than the 75 Mbps package I was previously subscribed to, so I made the switch and bought the least expensive modem I thought should be compatible to save money rather than renting. Even if I was only able to actually achieve 75 to 100 Mbps on a regular basis because of my limited channel number, I'd have been satisfied.

Is there a technical reason why ISPs couldn't allow an 8 channel modem on a 300 Mbps subscription? I could see why they would be reluctant because customers would compalin about data rates being below the advertised rates due to channel overcrowding. As I noted though, that's not the case here. I would be a happy camper with lower peak usage speed, since in this case, "lower" is a very relative term. Poor performance on my 300 Mbps subscription would match or outdo tip-top performance on a 75 Mbps subscription.