Lets look at this from a cost benefit/analysis point of view. Firstly, what is the benefit of doing 340 kts vs 250 kts inside 20nm?
- Saves about one minute
- Strokes pilots ego
Now what is the cost?
- Increased passenger discomfort through increased noise and a harder ride
- Increased risk of crew/passenger injury from turbulence (clear air, wake)
- Increased risk of Overspeed from wind shear
- Decreased manouvreability from higher TAS
- Increased risk of noise complaints
So I would suggest that on a cost/benefit analysis a professional airline pilot would probably choose not to fly at 340kts in the terminal area.