Pre-sales questions: Hardware choice and concerns about warranty paywall complaints

In regards to your modem choice. I'd push you more for a docsis 3.1 device. Reason why is we're seeing a push by ISP's to require docsis 3.1 for even lower speeds. For example, a couple months ago, Cox started requiring docsis 3.1 for speeds greater than 150mbps. Comcast is still only requiring it for gig speeds. I'm not sure who your isp is so its tough to give you a rough idea based on your isp. I know that your 150mbps should easily be fine with the cm600. But if you're going to upgrade, I'd look for a docsis 3.1 device. Tends to have a bit more tolerance for line issues as well. 

The R6700 is a solid router. You do see people on the forums with issues because its the forums and thats where people go with issues. 

but if you're using the WNDR3800 and its hitting all your goals, the R6700 is a good step up. 

In regards to the warranty. Its a touchy subject, even for those of us on here helping out. Support is free for the first 90 days of purchase. And devices are warrantied for 1 year (2 in some regions). But the issue is Netgear sells so many device and so many people call in because "its a router/extender/modem issue" when it usually isn't. So they do charge for support between the 90 days and a year. If it turns out to be a hardware failure, they refund it to you (from what I've seen/read/discussed). This encourages people to use the community forum or to contact isp's to fix problems first. And half the time, the community forum is faster/more knowledgeable than the tier 1 support. 

wish I had better reviews about the warranty/support option.