In my opinion we can define close range like this: Range where Marshall can 1HK opponent in armor with %100 health. That's close range. And close range absolutely ends where Marshall can't 1HK opponent without armor.
Perks used in that round are Low Profile, Maneuverability and Weapon Pro. However if you play with Auto-Armor, Maneuverability and Point Fire Enhance most of you can learn how to play godmode. Simply find the sweat spot while strafing and spraying at the same time where opponent becomes red indicating that your aim is on him and go. That's the only skill you need to improve.
Edit: There is no way you can be that accurate while moving while aiming down the sights.
There you go:
http://youtu.be/mN9wt5q_dZw