We are talking about Mark 4 Golf/Bora engines here, right? They are overhead valve, and a very similar design to the 300TDI. Maximum engine speed in a diesel is based on flame speed. The VW engines run higher boost, which gives more air and fuel to burn in the same space. These modified cars run around 25 to 30 psi. With the right fueling, this allows power at higher speed. Keep in mind that the guys running these high boost and fueling need to upgrade a lot of the internals of the engine if they want them to last.
Unfortunately taking a 300TDI to 30 psi blows the head gasket, so you are limited to the lower engine speed. If someone made better con rods and better head bolts, it might be possible. Or just buy a TD5.......