Generally if a car is tuned only, eg no other mods are done bar a tune, most of the gains come from a couple of pounds more boost and raising the AFR's from around the 10:1 ratio to 12-12.5:1. This is where most of the additional power is made along with some tweaks to timing and boost. Also, your car shouldn't be revved any more than about 5500-5900rpm as the power and torque curves will probably be ramping down by then. When my car was dyno'd the operator insisted on running it to the hard cut for the first couple of runs. I politely insisted he step off the go pedal after 5500rpm due to no more power or torque being produced. Needless to say he did so.