Ah...Google Fiber; we all can dream! Definitely check out the X6 and now the X7. I have fought with getting stable and high performance home networking for work & personal use with cable/other providers for years. The installation technology is finally catching up to where that is possible. I know some folks with TW service in other cities,...I'll ping them and see if that aspect has improved for them. For now, the only current gripes I've heard from people at my company that also thrive on high bandwidth internet for home-office is typically directed towards Comcast and ATT. I've fought my own battles over the years with Charter in NJ, MA, CT and later in SC; they seem to be finally looking more deeply at, and replacing older concentrators, etc...in the 2 counties here in SC where I've lived that were laid in when many subdivisions were originally staked out.
In general, 45MB on the downstream assuming it is capable of sustained throughput (nobody gives more than 3-5MB on the upstream but you don't need that for UHD4K or even HD) would be enough to sustain UHD4k...
The other issue in this age of rapid software development techniques, frequent releases of software with small improvements/corrections, etc...the providers of apps like Netflix, Vudu, etc...for HD/UHD HDTVs, BluRay players, etc...and the operating system developers for the devices themselves have their own issues they have to test for and find fixes that need to be released. I'm altogether too familiar with the "stutter" from Netflix even when bandwidth is high and sustainable at that moment; the apps seem VERY sensitive to minor time-out issues, DHCP IP lease refresh points, etc....sometimes even locking up and requiring restart of app and/or device and app. Ah...the joys of technology!