ENY is the value they use to figure perk points, it is short for vs ENemY. If you are in a 30 ENY plane, and you shoot down an enemy plane that is 5 ENY you get 30/5=6 perk points...which may be further modified base upon the outcome of your sortie, and also by the balance of the country rosters.
The lower the ENY number, the better overall comparitive performance that plane has. So flying a low (easy to fly) plane will earn perks slower than in a higher (plane that has performance drawbacks) ENY plane.
The country balancer system also limits the planes that are available to the country with the most players based on ENY value.
The OBJ value is similar except it is used to determine perks verses destroying enemy objects.
