The cat should take care of the backpressure issue. BTW, heres the link to Random:
Random Technology
Any good custom exhaust shop (local) should be able to set you up with a good stainless two-into-one pipe as well as the cat.
Exhausts are another story. Remus's rot, or rust out easily. If you live in the snow belt like me, consider something else. The three brands I recommend are Brabus, Eisenmann, and Supersprint. All are good chioces and at that point it comes down to personal taste. What are you looking for as far as looks and sound. Good luck.