I was playing with a rearend gear calculator the other day and it said with 4.56 you could get the car to 232 mph with 6th gear at 6000 rpms. I dought the car could handle that speed without major suspension mods.
I've had mind to 135 and couldn't slow down for $hit. I would definitely do a brake upgrade if I planned on going that fast very often (but like shaun said, it's a curser not a drag car
).