Two things.
First, in terms of it being relative, I mean to someone used to 10Mbps, 50Mbps might seem "extremely fast". To someone used to 50Mpbs, 100Mbps might seem "extremely fast". And to someone used to 100Mbps, 400Mbps might seem "extremely fast".
And second, by constantly changing, I mean just that. Just 2 months ago, my ISP's top speed for my "plan" was "up to" 50Mbps and we were getting about 60Mbps. But my ISP has changed and improved their service so now my same plan, as seen above, is giving us much faster speeds (over 100Mbps). In the 25+ years since I have had this same "plan" with my ISP, the top speeds have gone from 10Mbps to 20Mpbs to 30Mpbs to 50Mpbs and now over 100Mpbs.
So "extremely fast" depends on what you are used to, and that is likely to change as the Internet itself gets faster and faster.
Well, I started "networking" at 300 "baud". So when I upgraded to my first 56K modem, I thought that was "extremely fast" So again, it is all relative, and constantly changing.
Remember when 64K of RAM and 20MB of hard disk space was "More than you will ever need!"?