King springs sag so be careful what you instal .
They reckon King Springs sag but I've fitted them since 1995 and never had a sag issue. Kings have a lifetime warranty on sagging and can't imagine them handing out replacement springs indefinitely and never rectifying a sagging issue if it genuinely exists. Spring isolators relaxing and particularly strut tops on a Commodore collapsing has the same symptoms as a sagged spring.
Commodores have always had a great tendency for uneven ride heights left to right and I've swapped King springs side to side many times and hasn't changed eliminating a spring issue. My VF2 SSVR Ute has a 5mm aluminium spacer I made up and fitted under the RHR rear spring to even the rear ride height. BMW's are the best I've seen for even ride heights, perhaps some "badge price" is in the chassis jigging accuracy.