I have just had AT&T Fiber 1Gb installed. I connected my Deco x55.  I have 1 base station and 2 satellites (hard cat6 backhaul on each). 

AT&T’s onboard speedtestfrom the fiber gateway shows 1.3Gb down and up. A hardwired speedtest from my laptop connected to the gateway shows ~800-900 down and up.  A hardwiared speedtest to the Deco base station shows similar (~750-850 down and up).

But, when I connect via wifi (a couple feet a way, clear sight, signal strength showing between -30dBm and -45dBm), performance plummets, espeically on upload. Download I'm getting around 400-500Mbs. But upload drops to 20Mbps!

Ping and tracert on wifi end up with big latency swings. It'll bounce from 3-4ms up to 100-150ms.  This doesn't happen hardwired.

I did notice that (hardwired or wifi), whenever I run a ping test, the UI shows CPU Load spike to 65-80%.