Speedhacks flood the server with move commands. You don't actually move any faster than the server allows and it causes you to rubberband a lot. It gives you a slight advantage because if for any reason you would move less than maximum speed the server still moves you at maximum speed because an artificial program is sending those move commands. This is not exactly how it works, I am trying to explain it simply.
Also, players in the Enhanced Client used to move faster than players in the Classic Client. It has nothing to do with the server, all about how data is sent from the client to the server.
It's called interpolation and has been a required feature of online games since Air Warrior in '86 - the first fully graphical and latency sensitive client/server online game. Players often lost contact with the host, sometimes for seconds. Thus the host, using the player's last known control inputs, had to guess where they'd end up.
Yes, it was poorly implemented in UO but Origin, firstly, had no experience in online games and, second, the really good interpolation algorithms were soon tied up in court cases making improvements a mine field.
That's me being all cerebral and detached. But I what I feel when I see an exchange like this is anything but. It makes me sad because I know, in my bones, that the people saying such cruel things to each other are not hateful people. And, frankly, I must admit I watched virem11's videos. What struck me about them was how terrible I felt when the guy's Dread went wild and it was then lost, not just to him, but to the game. Everyone in his TS felt this loss.
I seem to remember one case of an unkillable player in UO but that was long, long ago. I do know it was a bug, not a hack. And, unless memory fails me entirely, the unkillable guy was the one who reported the bug. I know this might at first seem unfathomably odd, but being unkillable strikes me as one of those things that all of us would love....for an hour or two only. Well.....
Sorry, got distracted there. The host has your sanity checked info and you can't fool it into thinking you have, say, infinite HCI or DCI. Actually, the one client that could make it "wonder" what the hell you had is the EC as it allows you to swap out your entire suit in a split second.
Bottom line: if it takes professional athletes significant time to re-accustom themselves to the speed of their sport, the same applies to PvP in any game. We get accustomed to the sheer speed of it after playing it. Yet, oddly, we, as humans, are terrible at assessing the speed of activities unless we're currently engaged in them on an ongoing basis.