You can check it out at the start of the map when everyone spawns. Watch your teammates that run out with AR or Lacerator drawn that are in front of you, then switch to knife/spikes and see yourself gain on them.
I always draw knife/spikes to get to forward spawn faster.
Okay that is retarded. At least with the rocket launcher/GPMG there's some logic to it. The weapon and ammo are heavier, so you move slower. It's even more implied when the lvl 4 upgrade for soldiers is faster movement with weapon. So why would flicking out your melee weapon make you any faster if you're all carrying the same weapons and the same sized weapons?