If you're running stock differential and W58 on proper tire size, then I'm afraid I'm gonna have to call your bluff.
ive done 156 in my sc300 on 9a down a steep bridge i think i could have gotten to 160 if i was lucky but with out a down hill i top at around 150
Our cars tach out at 146-147 with stock driveline no matter how much power you add to the engine.
If you're running upgraded diff or tranny, then right on!
If you're running a wheel/tire combo that is too small in circumferance, your speedo is off by about 5%
NOTE: You can possibly squeeze 1 or 2 more MPH if you depress your clutch right before fuel cut, but I highly reccomend against this.
Handling can be adversely affected when you suddenly lose power to the rear wheels at 150ish