For me, Rifle in PvE is more or less only a Fun Weapon.
If i play "serious", i will always take Longbow.
Even when i play a power build.
All i would want is a small dmg increase.
The Trait [Crack Shot] should give +10% dmg if you use a Rifle.
At this moment, Warrior sprint is always better because of the 7% dmg increase.