If you want absolute full tilt max acceleration from a TDI you want the engine between 3,000 and 3,600 rpm (any higher and you will get better acceleration in a higher gear).

Most people find a TDI pulls that well from 2,500 rpm onwards that they don't need to change down a gear as often as you would in a petrol. It is called surfing the torque curve. As long as the engine isn't lugging at too low a revs you can get away with higher gears than you would expect (and get better fuel economy to boot).