When evaluating this type of equipment, one must differentiate between the device itself and other factors that can impact its performance. Blaming the manufacturer for issues likely caused by one's ISP is akin to saying, "I can't get past third gear because of all this construction on the highway... I'll never buy a Jaguar again!"
That said, the SBG6580 is a solid piece of kit.
This latest addition to the SURFboard line combines a DOCSIS 3 cable modem with a gigabit switch and a dual-antenna 802.11n wireless access point, providing all the networking equipment a home office needs in a single compact package... this amounts to a single point of failure, but that's par for the residential course. It can deliver 42 mbps downstream on a single channel (which my provider brands "Lightning") with support for eight bonded channels... meaning that when the day comes that ISPs start selling triple-digit speeds, this gateway won't need to be replaced.
Wi-Fi performance has been comparable to my old draft n router
with similar range and throughput in a mixed mode environment. What sets the SBG6580 apart are its better indicator lights and superior configuration utility which offers some settings normally found only on enterprise-grade equipment. Those less inclined to tinker should know that push-button support is provided; once the cable guy finished with the wall outlet, setup took less than five minutes.
Finally, one word of caution: the SBG6580 needs airflow. I originally placed it flush against a similarly-sized backup hard drive on my desk and found the unit hot to the touch after a few hours. To avoid problems, do not block the vents.