When accelerating, give it almost full throttle and center your shifts on 1750 RPM.
When cruising it is business as usual, highest gear you got with the slowest speed you can stand.
The
red dot curve that Daox put together looks suspiciously similar to the red dash curves on that tdi graph. My uneducated guess is that those red dash curves are the torque required for three different speeds (not labeled). And they come tantalizingly close to the "sweet spot" but I don't know if the stock gearing will get you there or not.