hello mate
forge oo7p allways work well combined with a remap,as far as the k&n 57i goes there a no go either a pipercross panel filter in a smoothed standard airbox,or a good induction kit where the filter is sat on the end of induction pipe sat in the wheel arch.57i is no good as they only sit on the end of the maf,inside the engine bay,(this defeats the object as they will only suck in warm air from the engine.
as far as the exhaust goes the most restrictive part is the cat,so either a sports cat/de cat is needed to free the revs up,milltek or custom made to fit your car is the way to go.
regards r-tech ben