Man i know i've maxed out my speedometer a few times on the highway in 5th gear at 20 pounds of boost on the Z32 transmission with a few hundred RPM to go before the fuel cut off.. (which means i was prob going 120 mph lol.. damn datsun speedo) 
  
 I just have a lowered suspension, air dam with a chin, air dam reinforcements and ducting and a BRE spoiler..  felt light but was a hoot =) 
  
 Sure the speedo is off..  dunno by how much..  but who cares..  scared the hell outta me.  
  
 I remember going to track days where the speedo was just past 135mph.. with a long sweeping left hander braking down to 110 mph or so.  a little under-steer.. but i think with a lower and stiffer suspension and some under body work.. it would be stable