I think Graphically each chocobo should have some physical representations of what stats they have.
Color - Each Color Represents a Region and Family of Chocobo.
Crown Feathers (Feathers on the Top of the Head) - Length of Primary Crown Feather denotes Age, Secondary crown feathers thus denotes Experience and overall Strength.
Tail Feathers - Length and bloom of the Tail feathers is determined by max speed.
Wing Feathers - Length and bloom of Wing Feathers determines stamina and total health.
Feet Style - Differences in Toe Number and Claw Size determine things like Increased Attack Power, Bonuses to Speed, and the frequency of being able to jump or use temporary speed boosts.
Beak Style - Size and shape determined by what types of things they have dug in, Long thin beaks good for wood and grass, while broad thick beaks are good for rocks and gravel.
Neck Length - Determines Agility and Dexterity especially when in combat. Also denotes Turn radius.