cutting springs doesnt make the spring rate any stiffer than it already is, you'll need to remake/heat them to make them stiffer. cutting springs just reduces the range of the compressions that the spring can make, so it gives you the illusion that it is stiffer. same amount of weight will still lower the car the same as before (as the spring will still have the same spring rate that it was originally wound to), only difference is that they'll bottom out sooner with more people, as they will reach their maximum compression sooner (at this point they'll just look like a cylinder with screw-type grooves).

you should only cut springs if you're absolutely sure you wont carry passengers, and you have measured it out to be the exact same length spring on each corner. but even then, its stupid to cut springs as you'll be affecting the bound and rebound rates (altho dampers are mainly responsible for this, theyre still attached to the spring and the spring does play a role in bound and rebound), and it will make your car's handling a little more unpredictable. luckily for me, you guys arent in south australia. i'd hate to see someone with cut springs take a corner too fast and see the rear randomly snap oversteer into someone else.