I ported this from amx to use on my server this can change a users speed, It's slightly glitched so that it goes back to normal after you change weapons well at least in ts. Please do not ask me to fix this I only ported this and thought it might to useful or fun.
Code:
/*
Fast Movement, v0.2
By Petey B thanks to KRoT@L
Usage: amx_speed <nick, part nick, @TEAM or *ALL> <Speed>
*/