Also, anything under 75kph seems to slow for me. Anything a light mech/medium can do to help late in the game?
Owens B is great.
Very fast thanks to the MASC, has C3 and the SRM rock the enemies screen so it can ruin their aim when fireing on your friends.
Just make sure you get behind cover fast if someone gets annoyed by you.
Owens C and Osiris B are good, too.
Don't try to kill your enemies, but rather cut off their arms and weapon pods and finish already damaged torsos. Great against BA, too.
Lights and mediums are useful in the late game, just make sure you never go out alone, and try not to drag attention.