You run slow as shit with that...but either way it's not just about having the weapon but having the right attachments and perks unlocked.
For example, my favourite setup after I hit level I think around 30:
ACR + silencer
Launcher/RPG
Scavenger pro - Pick shit up and extra magazines (pretty much never run out of ammo or grenades/claymores)
Cold blooded pro - invisible to uav, air support, sentry guns + no red name above head
Ninja pro - invisible to heart beat sensors + silent footsteps.
flash (or smoke if domination)/claymores
or I'll run the same thing but use the UMP or UZI instead to get a bit of a speed boost. I'm pretty much close to invisible at this point...and if you see me and chase you might just run into a claymore. And if you come back to the same spot looking for me you might just hit another =)
I love watching people run by me as I kill their teammates with this setup. Takes them about a second or two to actually figure out what's going on, by that time it's usually too late.