My parents AU fairmont used to do something similar too, would feel perfect below 100km/h but anything above it'd feel very unsteady.
In saying that it wasn't as bad as you suggest raven but enough to make the driver uncomfortable.

The shocks and springs were replaced for standard pedders equivalents and the ballpoints and bushes were perfect!

They put it down to the rims being measly 16x6s with 215/50/16 tyres on them...

After fitting Tickford 17x8s with decent Michelin 235x45x17 tyres, it feels a lot better!

Same with my EB, with 225/60/15 potenzas on the stock 15x6.5 rim the thing was glued to the road at speed!

After fitting the 17x8 AJRs with 235/45/17 tyres up front and 245/45/17s up back (which are considerably lighter) the car handles better then it used to but definitely doesnt feel as good at speed as it did with 15s

My theory is it's the weight of the rims but I'm probably completely wrong lol

Just some food for thought!

Im not say its like the front end feels like its going to take off, there has been a few comments about it being as bad as I say..... What I am saying is kind of like what your saying, its uncomfortable to drive in a way that you dont feel like you have full control of the car. At that speed I want to know I have full control of the front steering. She has sharkfins with 225/50r16's on it ( tyre spec for tickford rims).

No EF would have speed sensitive power steering. Only EL Ghias, NLs and DLs had it. As has been mentioned, SSPS is not working at such a high speed. I had SSPS on my ghia (until it grew to the correct number of cylinders)... it didn't have such issues.

When I drove an EL Ghia at speeds, the SSPS system was stiffer at 100km/hr compared to my EL Fairmont non-SSPS system. It could have just been me though.