[oldopelguy]

Quicker steering=harder to turn the steering wheel. That's OK for a sports car, but for the family cruiser they wanted little old ladies to be able to turn the wheel without building up arms of steel. In the Kadett there's also the potential for more weight on the front wheels, which would make them harder to turn, though I think the car weighs so much less overall that that's probably not a real issue.

I would say if you're driving a 1.1 Kadett you should absolutely swap in the GT steering arms for the quicker feel. On either a Kadett 1.9 or any Opel with wide front tires the issue would be how hard it is to turn the wheel. If you've ever wished for power steering, you want the Kadett arms, if you wish it was sportier feeling and your arms aren't taxed, go with the GT arms.

As to the rack differences I couldn't say, I've never gone further than the steering arms myself. It would be worth looking into, though.