I think the problem with 57i and other induction kits is that they intake hot air from the engine compartment which will reduce efficiency (cold air = better charge). You can rig up cold air ducting of course as the racing fraternity do. I use a K&N panel filter and rerouted the intake to a higher position to keep water and muck out of the system but retain cold air. Theoretically this should release 4-5bhp and a bit of torque. I think for best results a chip and a freer flowing exhaust, not just a tailbox, will give a bit more and should be noticeably better certainly in the mid range.
It was once said that the meek shall inherit the Earth, I have since discovered that the meek don't want it.