Example: Two Holden Commodores, Series1 3800s. One is a sedan, unmodified. Other is a ute (err pickup?) with a sports ECM. Acceleration difference is uncanny, the ute's power difference is very ferocious.
And thats just with a chip. K&N high flow airfilters make a noticeable difference too, and in the case of my Fiero, it had an incredibly short exhaust system and very short intake system - 10" from intake plenum to airfilter, and an exhaust system that was all of three feet long - which caused the engine to breathe VERY well and as a result had exorbitant pickup... if the car was still around I would be 'borrowing' the ute's sports ECM for added spicy power goodness!
Nick.