From the PTS, here is the list of our skills we can OE :
skill : success / SP / XP (for the +1)
Whirlwind : 97% / 528k / 5.28m
+1 power : Maximizes power of skill. Power increases.
+1 Cost : Maximizes the skill's efficiency. Decreases MP consuption.
Sweeper : 97% / 293k / 2.93m
+1 Power : Maximizes power of skill. Increased regeneration and a chance to absorb HP from a corpse.
+1 Power : Maximizes the skill's power. Increased regeneration and a chance to absorb MP from a corpse.
Stun Attack : 97% / 293k / 2.93m
+1 Power : Maximizes the skill power. Attack Power increases.
Blunt Mastery : 97% / 293k / 2.93m
+1 Power : Maximizes power of skill. Power increases.
+1 Power : Maximizes the skill's power. Increases critical attack power when using blunt weapons.
+1 Swiftness : Adds effect to skill. Increases Attack Speed when a blunt weapon is used.
Boost HP : 97% / 293k / 2.93m
+1 Power : Maximizes power of skill. Maximum HP is increased.
+1 Power : Maximizes the skill's power. The Max. CP is increased.
+1 Life : Adds effect to skill. Increased HP recovery rate.
+1 Bravery : Adds effect to skill. CP recovery rate is increased.
Fast HP recovery : 97% / 410k / 4.1m
+1 Power : Maximizes skill effect. Increases HP regeneration.
Polearm Mastery : 97% / 528k / 5.28m
+1 Power : Maximizes skill power. Attack power increases.
+1 Power : Maximizes skill effect. Increases the target.
Heavy Armor Mastory : 97% / 528k / 5.28m
+1 Power : Maximizes skill power. Increases P. Def.
+1 Life : Adds effect to the skill. Increases HP recovery rate.
Spoil : 97% / 293k / 2.93m
+1 Power : Maximizes the skill's power. Possible to use debuff to reduce Atk. Spd. The succes rate of debuff is increased.
+1 Power : Maximizes the skill's power. Possible to use debuff to reduce current HP and the succes rate of debuff is increased.
+1 Earth Vulnerability : Maximizes the skill's elemental effect. Weakens target's earth resistance.
Hammer Crush : 97% / 410k / 4.1m
+1 Chance : Increases success rate. Maximizes the skill's success rate.
+1 Cost : Maximizes the skill's efficiency. Increases effectiveness and decreases MP consumption.
+1 Fire Attack : Maximizes the skill's elemental effect. Increases fire damage.
+1 Water Attack : Maximizes the skill's elemental effect. Increases water damage.
+1 Wind Attack : Maximizes the skill's elemental effect. Increases wind damage.
+1 Earth Attack : Maximizes the skill's elemental effect. Increases earth damage.
Spoil Festival : 97% / 293k / 2.93m
+1 Power : Maximizes the skill's power. Possible to use debuff to reduce Atk. Spd. The succes rate of debuff is increased.
+1 Power : Maximizes the skill's power. Possible to use debuff to reduce current HP and the succes rate of debuff is increased.
+1 Earth Vulnerability : Maximizes the skill's elemental effect. Weakens target's earth resistance.
Wrath : 97% / 528k / 5.28m
+1 Power : Maximizes power of skill. Power increases.
+1 Cost : Maximizes the skill's efficiency. Decreases MP consumption.
Wisdom : 92% / 3.78m / 37.8m
+1 Power : Maximizes skill power. Increases hold tolerance.
+1 Power : Maximizes skill power. Increases sleep tolerance.
+1 Power : Maximizes skill power. Increases mental attack tolerance.
Health : 92% / 3.78m / 37.8m
+1 Power : Maximizes skill power. Increases poison tolerance.
+1 Power : Maximizes skill effect. Increases bleeding tolerance.
Parry Stance : 92% / 2.94m / 29.4m
+1 Power : Maximizes skill effect. Increases physical/magical P. Def.
Earthquake : 92% / 2.94m / 29.4m
+1 Power : Maximizes skill power. Increases effectiveness.
+1 Cost : Maximizes the skill efficiency. Decreases MP consumption/HP.
+1 Earth Attack : Adds attributes to the skill. Increases earth damage.
Armor Crush : 92% / 2.94m / 29.4m
+1 Power : Maximizes skill power. Increases effectiveness.
+1 Cost : Maximizes skill efficiency. Decreases MP consumption/HP
+1 Chance : Maximizes skill efficiency. Increases success rate.
Polearm Accuracy : 97% / 586k / 5.86m
+1 Power : Maximizes skill effect. Increases accuracy.
+1 Cost : Maximizes skill efficiency. Maintaining MP is decreased.
War Frenzy : 97% / 293k / 2.93m
+1 Power : Maximizes skill effect. Increases tolerance to shock/sleep.
+1 Cost : Maximizes skill efficiency. Maintaining MP is decreased.
Master of Combat : 92% / 3.78m / 37.8m
+1 Power : Maximizes skill effect. Increases attack power of sword/blunt weapon/spear weapon.
+1 Power : Maximizes skill effect. Increases attack power of dual-bladed/fighting weapon.
Braveheart : 92% / 2.1m / 21m
+1 Power : Maximizes skill effect. Increases the amount of CP recovery.
As u can see, skills 76+ are now able to OE, but the cost is very expensive.