I've done 165(on speedo) in 5th gear at about 7500 with a tune and exhaust mods only. Car definitely has more than that in it.
Ah ha! That's more than factory power you see.... ; )
I threw my calculations into a simple spreadsheet. LOTS of assumptions, but it gives you an idea of how drag on the car in this region acts like an incompressible fluid and is proportional to the square of the speed of the car. So each mph requires more and more power.
Here's what I came up with... feel free to throw spears. Even with all the shortcuts I took, I'd still bet it's within 5%. Bottom line this car is going to be difficult to get over 180 without a power-adder or major aerodynamic enhancements:
Stock: 164 mph
Stock+Tune: 168 mph
CAI, O/R X-Pipe, Tune: 170 mph
CAI, Long Tube Headers, O/R X-Pipe, Tune: 173 mph
Cheers
Lego