A couple things to remember. On a VE pump fuel system there are three pressures. One is inlet pressure (from lift pump). The second is internal timing pressure. The VE has a vane pump built into the front of it. It creates a varying internal pressure that works against the timing piston, which allows for the injection timing to vary depending on RPM. The third is the injection pressure.
Running a higher pressure electric lift pump can have negative consequences since it pre-charges the vane pump. This can mess with the timing pressure and alter the timing (advance it too soon/low in RPM range). If you use an electric pump, keep it low pressure.
On really high-horsepower applications (like, Cummins 6BT with 4000 RPM) keeping fuel pressure at 6-10 PSI at the inlet becomes a problem just due to the tremendous volume of fuel used (12MM pump, 6 cylinders, BIG injectors, lots of fuel) and people run large lift pumps. The only way to tell if this is an issue for 300TDIs would be to put a gauge on the inlet and see what happens. On my Cummins project I am running an updated mechanical lift pump that is regulated to 14 psi, and I don't think that pressure has any effect on internal function.
A lot of Volkswagens never even ran a lift pump, and relied on the vane pump to pull from the tank, but again, that would change the internal timing function since it would probably lower the case pressure.