Head Rush restores some health every time you kill with a headshot. It is a Tier 5 Ranged skill that pays off for accurate players, especially in Horde fights and Marauder camps.
Yes, it is one of the best late-game Ranged skills if you aim for the head.
Focused Shot, Deadshot and Iron Grip.
In Horde fights, aim for the heads of the leading Freakers. Each kill gives you a little time and a little health.