Keep in mind that Gearing Commander is just a reference.
It states what the gearing is capable of...not the bike.
Engine/hp, rider, rider size and weight, tire condition and size, weather/temp/humidty/wind/ect. all play a big part in just how fast you can go.
If you're a serious land speed racer all this is very important, and you already know it.
If not, as said above, the speedo is not accurate stock anyway. A Speedohealer and/or gps will solve that.
Most of us can easily do 150mph in around or just over a 1/4 mile, and then you have to have room to slow down.
To go 170, 180mph+ is going to take around a mile or more...and much more room to slow down.
Consider 60mph you travel about 88 ft per second, now do the math for 3 times that. That's nearly a football field in a second. Puts things into perspective.
A +3 rear sprocket will still let you do 170's, and give you a noticeable boost in acceleration.
All depends on what you want.