Well, I don't have much of an opinion as to whether speedhacking is a myth or not, but I'm 100% positive that movement speed is not the major benefit of speedhacking. Speedhacking affects the data stream to reduce or eliminate the delay between swings or spells. A rumored secondary effect of this is that people in the vicinity of a speedhacker will start to lag. I believe I have observed this, where I'll be lag free all night, then all of a sudden I'm attacked by another player and my screen starts jumping around like crazy - but again it's just an anecdotal observation.
My computer hardware has never been cutting edge and I spent years of my UO life playing via dial-up, then satellite (talk about latency), then various DSL connection, and finally just a couple months ago I switched to a super fast cable connection. I'm zooming around as fast as most other people now, but whenever I've seen people run circles around me, speedhacking never popped to the front of my mind. However, when I've maxed out stamina & SSI to cap swing speed and someone swings twice as fast as me, or when I've capped FC/FCR and someone casts spells way quicker than me, or when my screen starts hopping around with lag as soon as someone attacks, then I think speedhack. I can hold my own in PvP and have a good idea of to max out a template; and some people are clearly fighting outside of the limits.
Let's just say, I don't think the UO developers would make such a big deal about fighting speedhacking (they included it in the main UO Herald announcement of things they are working on you know) if it wasn't a pretty big issue they felt they had to deal with. Maybe they should re-phrase speedhack to illegal scripting, or something like that they are trying to fight.
