I did an experiment with both my WoW accounts wondering what it would look like as a player observing a speed hacker.
I ran the speed hack on my vanilla WoW account and ran my main account normally; dualboxing.
Running the hack at full speed I zipped past my main and only caught a glimpse of a toon and it went by so fast I couldn't see the name at all.
I then turned around on my hacked toon and zipped past the main going in the other direction and my main didn't see anything at all.
Running the hack at 2x, my main observed that the hacked toon would run in place briefly then pop up about 5 yards or so in front. I remember seeing players way back in my noob days of WoW displaying the same behavior and back then I thought, "Whoa, that dude must have a real shitty connection..." and now I realize they were probably running a speed hack ^_^.
So how detectable is this really?
If you run it full blast, a person caught offguard who catches a glimpse of you could easily mistake that you just logged into the game and probably won't be thinking "ZOMG HAX!"
And, the only way you would know for sure if a person is speed hacking is if you know what to look for...... i.e. you are already aware of speed hacks and probably use them yourself.
On a side note, I also used the hack on my vanilla account in a WSG match (2x speed nothing more).
After the match I had some dude whisper me that he, along with a few others, had reported me for using a speed hack.
Well, its been a week later and I haven't been banned or anything.