Mine has the K&N which sounds fabulous but I understand that you lose a few bhp when it's hot because the position of the filter just downwind of the radiator means it draws in hot air which is less dense and affects power. To counter that I have fabricated a box that shields the filter from the radiator so I should be getting close-to-standard power and a lovely noise too.
My son has a 182 Cup and reckons the best set-up for power is the standard filter box fitted with an ITG panel filter and a Samco hose for the elbow into the plenum to smooth flow. Ktec sell the Samco hose for about £80 but someone on Cliosport reckons they can source the same part fo about £50.
Itg panel filter (personally prefer foam ones and ITG is better quality than pipercross imo, had pipercross one on Trophy and previous car and the foam around the side fell apart)
Espace v6 airbox with k and n filter and samco hose. Basically a cheap Maxogen. Personally i think its a better setup than my standard airbox with itg panel filter.