At last I can shed some light on the matter, still weird but very acceptable.

Hooked up the Temp Gauge last night and had it idling in the garage to test the system and the new fan switch before taking it for a drive.

On Idle Temp was running at a maximum of 75 degrees before the fan kicked in, fan is on for a short while and then switches off, at least I know the fan is more than sufficient to do the work.

When doing normal town driving at 60-80km/h, the temp is sitting between 68-72 degrees with robot stops included.

On the Highway it stays at the 68-72 degree range until you stop at a off ramp, then it climbs to about 75 degrees, after that it doesn't really come down on the highway, until you drive into town sections, within a kilometer it goes down to the 68-72 degree area. - Weird part, maybe heat soak, pressure, I'm clueless. But the temps is so low, it is not going to bother me anymore.

Lessons learned:
1. Stock Gauge and Temp sender is very good
2. If you need to replace the stock temp sender with a pirate one (Especially RSA) rather buy a new gauge and sender that reads degrees rather than just a low and high scale.
3. On installing a different radiator, install a new Gauge.

I highly recommend VDO gauges.

Thanks for all the help and suggestions.

http://www.cruisecooler.com/Cooling%20Tech.html
Here's an interesting piece to read.

The reason I am saying too high flow through the radiator is the following info I have:
My wife's car is a VW CTi ( the South African guys will know what car this is). It is a reproduction basically of the old 70's VW Gti Mk1 with the 1800 injected engine. Well, anyway, it's radiator got a crack and I needed to replace it with a new one. Upon removal and fitment of the radiator I noticed the core consist of pipes that are something like 10mm in diameter each. Comparing this to the fine piped core of the datsun and even my Nissan car, I would say that nissans have a thin piped core to slow down flow through the core because as we all know, water flows very slow through a straw compared to a garden hose.
That is why I lean in the direction of too fast flow.

Find someone with a infared temp reader to check your temp gauge is reading correctly

If its jammed open just check if the water is flowing when the motors cold. Easy

im starting to think too much flow as well, it is a plausible effect from the cause. but that would mean the thermostat would be jamed open on the freeway, from the heat in the coolant.

With a fully pressurised system the motor can run up to 110C quiet safely and it is not overheating, above 120C start to worry.

Only the stock datto grill infront of the rad.

1200GX, i'm also leaning in that direction, or pressure.
Will have a better overall view when I can see actual Temp readings.

On highway (freeway) driving the temp is not suppose to go high at all as there is sufficient wind that goes through the radiator.

This is really baffling me. I am trying to think what it can be but without us standing next to the car it is quite difficult to figure out.Is it possible that the water is circulating too fast when you are driving on the highway (freeway) with higher than city driving revs?

is there anything restricting airflow infront of the radiator?