R8000P not producing gigabit wifi speeds

the R8000P has a 3x3 antenna setup for both 5ghz bands and 2.4ghz. It also has mu-mimo (multiple input, mulitple output). Meaning it can talk to more than 1 device at once if those devices support mu-mimo. And most wireless devices are only 1x1 or 2x2 devices. 

so its not a simple answer. Can it do more over the 5ghz if using more than 1 device? potentially. 

but it usually doesn't need to. And it half the point of triband was having the ability to seperate out your high bandwidth device. 

The reason I say it doesn't usually need to is most services don't need 400mbps. For example, 4k streaming is only 25-40mbps needed. So even if its buffering, its not going to get anywhere close to the 400mbps available. 

I've ran triband and dual band flagship routers. with the triband having 2x 5ghz bands (and not being to far away) I haven't ran into bandwidth issues. And I've tested using multiple 4k streamers and gaming machines at a time. 

I'd recommend reading one more article, its a review from smallnetbuilder on the r8000P. its a well written article 

https://www.smallnetbuilder.com/wireless/wireless-reviews/33147-netgear-r8000p-nighthawk-x6s-tri-band-wifi-router-with-mu-mimo-reviewed