Not being funny mate, but why are you chasing such high top speeds? just seems you'd be spending lots of money to get there mate.
I've got my 172 FF to just under 140 on the speedo, then realized just how fast i was going and slowed right down!!
There fast enough imo, unless you want to lose your license.
haha im just curious, anmd wonder what the gearing allows thats all and what its rated too..