I cant stand how the term "back pressure" has crept into the car world and fear mongers people into not doing exhaust modifications. as long as you dont do 3" piping on anything under 600hp you'll be fine. 2.5" is pretty big in fact but its the aftermarket common.
And Mcrews, are you an airhead? My car has a headers back full exhaust system. Its a fairly common term to tell people that you have a complete exhaust system. Meaning exactly what randomfact314 said he had. Headers and aftermarket piping to an aftermarket muffler. Manifold back means the car still has the stock exhaust manifolds but has everything else. And NO you don't need catalytic converters to have a cat-back system. Its merely for reference against the stock formation. Google cat-back, what do you find? The rear most section of the exhaust system after the piping where the stock cats are welded into. My set up is long tube headers to an off road H-pipe to a Borla cat back system. Even Borla calls it a cat back system
Stainless Steel Cat-Back
And to randomfact314, id change your exhaust closer to stock. Only because ive seen smaller engine cars loose power and efficiency. They gain with a new dyno tune but on the factory tune its hit of miss with more misses than hits. But you could probably keep the header. Long tube headers gain torque.