the 5th gens are fun cars and even the z needs some help it was tamed down for street use, I was lucky enough to build and maintain several 5th gens, we raced then all over the US in the Optima series .....I think the basic
DSE Speed ! kit would help you the most, it adds springs and better sway bars and you keep the z dampeners
here is the some of those cars
this one has the full DSE speed kit 3
this one we kept the stock z dampners and use the DSE speedd kit 1
this one we used Phadt and it sucked so it was changed to ridetech