Your still looking at around $4000 (fronts only) for an AP upgrade, where you can get a set of Brembo's (GTR not F50) for around $2,000 and another $600 for new pads, rotors and lines. Personally I think the GTR option is better and is what I'll be doing as not only are the initial costs lower replacement pads and rotors are much easier to get a hold of. I have not driven in a car with an AP upgrade so I will not comment about their performance but with decent fluid, lines, slotted rotors and track pads you should be fine for most track days. However with the current dollar, off the shelf Brembo's are a lot dearer than AP. I have also heard from people in the business Brembo's have better dust seals for road use but require more reconditioning if being used hard on the track.