The maximum boost for selected parameters and effects is as follows:

Parameters: 400% (HP +10%, etc.)
Damage boost to enemy type: 300% (Man-eater, etc.)
Boost to equipment when wielding one weapon in both hands: 300% (True Doublehand, etc.)
Boost to equipment when wielding two weapons: 200% (Eternal Wind, etc.)
Fill to LB gauge every turn: 1200 (Auto-Limit, etc.)
LB gauge fill rate: 1000% (High Tide, etc.)
LB damage: 300% (Heart Overcoming Hatred, etc.)
Jump damage: 800% (High Jump, etc.)
Physical/magic evasion: 100% (Evade, etc.)
Boost to parameters of espers evoked: 300% (EVO MAG +10%, etc.)
Boost to parameters when setting an esper: 200% (ST Reflection Boost, etc.)
Boost to evocation damage of espers: 300% (Frigid Evocation, etc.)
Common item drop rate: 100%
Rare item drop rate: 100%
Accuracy: 100% (Five Lights, etc.)
Reduction of encounter rate: 100% (Model Chocobo Rider, etc.)
MP cost reduction: 80% (Vigor Voice, etc.)