Exhaust setup won't increase much... probably around 5% which is noticeable on paper je..peak torque/power remain about the same, probably response on the graph might be different
Imo..Century acceleration time only useful at drag strip and traffic light/toll je for daily usage...overall performance matter for daily drive.
I send in dyno for base figure, engine check, and how's it's power/torque graph..then from there I decide which mod should I go for, setup my shift light, rev limiter and etc
Ps: knowing your car capability, you know which car you can play with and Which car you need to give way