if you are using a laptop via wi-fi you will not get the posted speeds, The 800-900 speeds are only valid on an ethernet connection. Secondly, which most people forget is that you must also have a gigabit ethernet port, otherwise it will top out around 104 mbps.
It's been a terrible experience so far. Waited forever to get a tech out to install. After a day I was getting slower speeds than when I had 75/75. I'm standing several feet away from the router and I'm not getting past 90mbps for my gigabit experience. I had tried rebooting and it didn't get any better. Also tried to contact Verizon and had to navigate through all the menus to end up with no help or solution.
For me, it seems like gigabit internet is essentially just 8 shotgun connections at 100Mbps. I get no congestion and I get decent connection speeds for me. I don't get 840Mbps up all the time (sometimes about 400Mbps+) but with everything hardwired in, I don't complain since nothing seems slowed down.
With my work VPN, I was getting 4Mbps to it with my 100Mbps connection but now it seems my max speed is 40Mbps.... and that's fine because work isn't too demanding on my network. But while I'm using it for work, I can stream TV with Hulu TV at HD rates (I think about 20Mbps) and Skype, etc. is unaffected by any of that. Dropbox works just fine at all levels.
So if you're expecting constant 840Mbps speed, you won't get it probably but if you hardwire as much as you can, you'll get consistent 100Mbps speed up and down on most devices almost all the time and you won't run into concerns about saturation of bandwidth.