lol its not that nitrous cars are slow in general its just that car was slow period,no matter if it was all motor,nitrous,turbo his combo is not good.
lotta factors but lets say he was going 123-124 on a 150 shot,different brands market there kits different,nos is rated at flywheel,nx is rated at rw.that bieng said a 150 nos shot will give you aproximatly 110rwhp where as the nx should give you around 150rwhp,big difference.
your car on motor is stronger than his on motor,him off the gas will probly trap 110-114 depening on the rwhp shot he has.
your car on the bottle that is jetted for a 150rwhp should go 130,wich is not slow.hope that helps