For street/AX/light track duty, the M030 is more than enough and generally affordable.
But if you want the best performance, an adjustable coilover like the PSS9 is the way to go. Of course, they are somewhat expensive and will rattle your fillings on the full hard setting (save the full hard setting for serious track days). On the soft setting, they are reasonably comfortable on the street.
If you opt for the PSS9's and then put on some sticky street tires, you'll next find that you'll want stiffer roll bars. The 996 GT-3 adjustable front and adjustable Tarett rear bar will fit the bill.
Then, you'll want more camber and lower adjustable control arms will take care of that. While you in there, might as well install the adjustable rear toe arms too so you can get it all into proper alignment.
Then, .... well, you get the idea. Its a slippery slope.
