Well do you want a slight induction roar or not , if yes get a 57i if not get a panel filter. A 57i will cost £80ish the panel will be about £35 If you go for the panel one you can put a cool feed to the air filter box [ look at how too's ] I think K&N have the edge
BILSTIEN DAMPERS, 4-2-1 MANIFOLD, HEAD WORK BY SABRE.