My good friend has AT&T fiber to door: 300 down, 300 up. He has no problem clocking that.
Before my upgrade, I had 400 down and was able to clock +20% most of the time.
Not sure how fiber to house then what kind of modem and its speed along with a router. I have triband gigabit router.
By the way, what do you used to measure and how, wi-fi or ethernet? This can be a choke point. My laptop a 2x2 AC card will not get 800. My old iPhone 5SE can clock 300 on the 5Gig band.