I really don't like "Magnitude and Direction" or "Terminal Velocity." While "Magnitude and Direction" may seem descriptive and fitting to math types, it's nearly meaningless to us non-mathies. Sure, I know what "magnitude" means and "direction" means, but how they apply to a distro escapes me. Believe me, this techie-insider stuff turns off the vast majority of users, who are decidedly non-techie and don't wish to be so.
"Terminal Velocity" is, if anything, even worse. How many people know what a terminal is? How many prospective users have a burning desire to deal with terminals, even if they know what a terminal is? Most non-techies are scared to death of terminals. If you want to talk about speed, say "speed," not the rather pretentious "velocity."
I think "Speed, Performance, Stability" is pretty good. I also think a slogan isn't something on which the fortunes of VectorLinux will rise or fall.