I can't take credit for that, it was Mozambiquer.
The boost levels at cruise are not unusual for a stock-bodied TDI... Yours could certainly stand for a bit more without increasing the fueling, it will certainly reduce your EGTs.
One way you can quickly and easily do this is - if you don't already have a 3 bar MAP sensor or tune for it - to install one directly in place of the stock 2.5 bar sensor without remapping. This will effectively increase the requested absolute pressure by 3/2.5 or 20%. so, 4 PSI gauge will be (14.5+5)*1.2=22.2 PSI (absolute), which equals 7.7 PSI (gauge, at sea level).
Be very careful though - 22 PSI originally requested by the ECU mapping at full boost would become 29.3 PSI!
As for the mileage, I think it's in the ballpark of where it's supposed to be given the tires and aerodynamics of your particular vehicle. Swapping in a BHW bottom end will not really help you in this regard.
PS: I don't condone swapping in a 3 bar MAP sensor without re-mapping, even this is exactly what I have been doing for the past 6 years on my own car. Try this at your own risk. The proper action, once you have determined that the EGT responds desirably to more boost as suggested, is to have the ECU remapped.