stat and what they really translate to in map?

[user001]

what i meant by the title of this thread is.. for example 350 atk power deal like 4k on pve ..if i add a atk gem +28 .. is the increase in pve dmg a lot? or if i upgrade my weapon and + 5 atk power to my total stat.. how much does it bring actually.. like how much is a lot of increase 10 ? 100? 

and what about the +28 dmg gem instead of atk powe gem? hope guys understand what am i rambling and trying to ask =)

 

and is the lifesteal gem in game alrdy instead of hp heal when crit