Speed proficiency

Does the Speed proficiency make a big difference and does it make up for the loss of lightweight on Sub machine guns? And do you notice the difference on Light machine guns? or is it not noticeable enough to be affective and be a "replacement" to the Lightweight Perk that was in MW2?

While not as dramatic as the lightweight perk it definitely does make a difference. A player's run speed is based off of the 'mobility' stat of each gun. It can still help balance some of the clunkiness of an LMG.

As far as effectiveness, movement speed is one of the best defensive stats in the game. The ability to get behind cover, flank, and the speed at which the enemy has to aim all makes it a viable choice. As you may recall from MW2, player with lightweight are always harder to kill.

You can equip the Speed proficiency only with Light Machine Guns, Sniper Rifles, and the Riot Shield.

It makes up for the slow-down in player speed while using these weapons. It is practically the same feature as the Lighweight in other MW games.

Sub-Machine Guns and Shotguns don't get any speed gain from this proficiency.