I'm just starting on the road to 'pimping' my Vectra C 2.2 petrol (LS), starting with an induction kit and stiffer springs. Does anyone know the how much extra HP i should be getting from the K&N 57i kit? I've got some Apex springs on order that are (according to the supplier) ok to use with the standard shocks, but may shorten their life, any ideas on how much by?