If you get speed 3 capped ASAP (level 11-13). It will get into the mid to high 70's on its own by level 40.
12-16 SP goes a long way towards getting AGI and Vision up. Lbs need so much other stuff besides speed, it'd seems like it would be hard to get a balanced build going that way.
But I've never taken an LB beyond level 14, I just run the virtual player builder a lot, so take it with a grain of salt.