Humans dont feel bhp very well , they are more sensitive to torque but even then its very hit and miss
This is my dyno chart* - firstly the 370z wont make 326hp at the flywheel on many dynos , mine made 299hp after fitting a cat back exhaust and intake , I never dyno'ed it stock
After the remap it made 309hp at the flywheel
Removing the stock cats had a big impact getting up to 345
In real terms I ran the car down the drag strip in a variety of guises , stock it ran 13.8@101 (Partly limited by the awful Bridgestone tyres), after remap it ran 13.5@105 and after the cats were removed it ran a 13.3@108
If I had my time again I would put the money into fitting a decent diff , that will make much more impact in performance terms than any n/a tuning
*my car is an auto so makes a little less on the dyno than a manual