Wireless Performance - more
5 GHz seems to be the one bright spot for the ZyXEL's performance. In the 5 GHz downlink test, the NBG6716 started out significantly faster than the TP-LINK and remained there out through 9 dB of attenuation. Both devices performed well throughout the range with the TP-LINK having a clear edge over the ZyXEL beyond 18 dB of attenuation. Visually, the line that's highest and the farthest to the right is the winner. Clearly, for this test, the Buffalo and the TRENDnet routers were wrestling for third and fourth place.
5 GHz Downlink Performance vs. Attenuation
For 5 GHz uplink, the story is pretty much the same. The ZyXEL starts out on top, but after 9 dB of attenuation, the TP-LINK outperforms all three competitors. The Buffalo WZR-1750DHP has the poorest showing in this test starting out below the other three devices with its graph remaining "below and to the left" of the other three devices throughout the test range.
5 GHz Uplink Performance vs. Attenuation
The Ranker Performance Summary below shows the NBG6716 ranks #8 of the ten AC1750 class products currently active in the Charts. It's no surprise that it scored poorly on the Routing throughput - its simultaneous routing throughput was lowest of all routers within its class and the #8 ranking in that cateory was buoyed only by routers achieving fewer simultaneous connections.
If you look at the Average and Maximum wireless throughputs, you'll see that the ZyXEL scored at the almost-bottom and bottom of its class for 2.4 GHz downlink and uplink tests.
The relatively good 5 GHz performance noted above helped the ZyXEL rank #4 for 5 GHz Average downlink and #1 (!) for maximum downlink throughput. The #6 total ranking for Wireless Range was established by three of the four benchmarks, with only a #2 rank for 5 GHz uplink range as the bright spot.
Ranker Performance Summary for the ZyXEL NBG6716
So is the ZyXEL worth a buy? If you want a StreamBoost-enabled router and plan to primarily use the 5 GHz band, then yes, the ZyXEL is a better pick than D-Link's DGL-5500 and they cost about the same. If you don't care about StreamBoost and want the cheapest AC1750 option, you might look at the TP-LINK Archer C7. Its current low price could be driven by the need to clear out stock in preparation for a new version, so keep that in mind if you go that way.
But most people buying this class of router are looking for performance and for that, it's still hard to beat the ASUS RT-AC66U, despite it being the highest priced option in its class.