mine is remapped and I run a K&N rechargeable air filter - which does seem to make a difference.. got it real dirty 6 months back and put a paper one in for a while - now breathing better with the K& recharged and I swear it is giving better mpg.. hard to tell without a trip comp though
noticably better take off with the engine remapped..
Dont forget if you chip it you may need to swap manifold bolts moore power develops moore heat, and so moore expansion, which can and will snap the old bolts. I think they use longer bolts with some form of spacer to absorb the expansion