top speed will increase in most occasions...

depends where peak power is, and if you can hit the limiter in top, almost all cars cant, so more top end power will increase their top speed.

hence how skylines can do well over 200mph on standard gearing when modded.

dont take a fucking genius to notice that. you think every RST or Cossie that can go faster than their standard top speeds have had their gearing fucked with?