But even regular freeway driving I am still running at at 3/4 gauge and I have to ease off the throttle to keep the temps acceptable on hills. It will drop to half on the downhill quite quickly so it really does seem as though the engine produces more heat than the cooling system can cope with when under heavy load. Of course I have the additional problem that my egt's hit 1200 with no problem under any sort of freeway driving.
Other thing I think your missing is the fact that factory 1.6TD did infact have an auxilliary water pump that switches on at 104°c but is not there to aid cooling but to prevent heat soak when the engine is turned off, on syncro models this switch is also linked to the turbo cooling fan fitted behind the left hand rear light that blows cool air from the rear pillar over the turbo.