couple o questions

i know that aem is probably the best cai out there, but how do the dc and the injen hold up too it, they are both around $30-40 cheaper?

also im looking at headers and im not sure why i should spend an extra $90 on the polished headers, is the difference between the polished stainless steel and the ceramic coated really that much?

lastly whats a good exhaust system thats moderalty priced, i like the price of the a'pexi dunk series, but how does it hold up to say the greddy evo and the a'pexi n1?

thanks