Your bearings will indicate by mileage whether they should be replaced.

The Calibra setup is very old fashioned small diameter and bad design for side loading. Previous comment on the steering knuckle (bearing housing) is important if everything else has been ruled out. These can be deformed by kerbing, even the ball bearings can be crushed and flat sided. If you had the leg off -  for the price of the bearings to be pressed out and new pressed in and if the Calibra was high mileage might have been a good idea if it had to be done eventually.

You will never gauge the bearings wear when they are cold, when cold any movement is a sign of the start of a bearing collapse. As a mechanical engineer you would know that vibration turns to audible frequency that you can hear and feel, if the problem is at 90kmh there is a sound? the frequency of that sound in Hz is the revolutions of what is worn - lets hope it´s not your differential (pinion) which is turning around 3.46 times faster than your wheels. it is a rotational problem you have and not a clunk (which is top mounts)?

I have a rear bearing that starts whining after 2 hours at 60+ mph, just as everything has heated up to maximum. otherwise you would never notice everyday.

I thought of reporting back one final time to inform about my findings. I think I managed to nail down the issue and hope it is resolved. One of the bolts on the steering coupling was sitting more loose than required for some reason. It did not cause any play in the steering, nor did it produce any noise whatsoever, but I suppose the looseness was sufficient to cause an uncomfortable feel.

True I spent few hundreds of euros switching other things that were not the cause (shocks, lowers arms, tie rods, 2nd hand steering gear)... but seen the mileage those may have come up sooner or later as well.

Cheers to all for the help!