What contributes to mon’s performance metrics? Does IV have any effect?

Question

In soulsilver/heartgold games, they added performance metrics (speed, power, skill, stamina, and jump). Does IV have any effect to the metrics? Because I have couple with same perfect IV stats and same nature/personality, but they seem to have different performance.
Can they ever be increased or decrease?
Do they have any influence in battles or is it only for Pokemon contests?

Answer 1

A Pokémon's ability in a performance stat can range from 1 to 5, though the maximum value of a given stat is determined by the Pokémon's species and is often lower than 5. The maximum values are unrelated to the species' base stat total. The default value for a given stat is also determined by the Pokémon's species, and the actual value varies further on a daily basis based on the Pokémon's Nature. In order to maximize a performance stat that is not already at the species' maximum value, the Pokémon can be given Apricorn juice, which can be made with an Apriblender or purchased at the Pokéathlon Dome.

The day-to-day performance of a Pokémon in the Pokéathlon changes based on the day of the month, their Nature, and their personality value. The extent of the change may increase or decrease an attribute by up to 4 stars, subject to the Pokémon's species minimums and maximums, though changes beyond 1-2 stars in either direction cannot be achieved without Aprijuice.

Performance has no effect in battles.
source and effects of natures on performance
effects of personality on performance