[OwenM]

Maybe the engine tuning theory I leaned 20 years ago is rusty, but as I recall slightly lean mixtures actually produce the most power, more then slightly rich mixtures, so adding extra fuel does not help power unless the mixture was very lean to start with.
Manufacturers are VERY unlikely to use lean mixtures for wide open throttle as it could lead to engine damage due to high combustion temperatures, no way that could be tolerated in a production engine as it would affect reliability.
Foam air filters like the Unifilter are large and occupy a significant area in the air box, they can have an effect on the damping and resonance of the intake system which can in turn affect power output.