Stillen makes a nice set-up ( got full cat back ) and HKS's is also very nice, more of a preference thing. I would recommend a larger diameter piping, with a stright though design. I also would hollow the cat, or get test pipes .
In terms of intakes, they all do similar things, the big japenese manufactors ie hks greddy... are all fine, Jim Wolfe Technology is a great company for 300z intakes, and in any type of parts in general, he knows his Z's.