The x pipe should go right after the headers. And yes I would get some decent headers on there, you dont have to go really high dollar, I had some Summit cheapos for a long time and they were fine. I agree on the 2.5" pipes, a little extra back pressure helps with torque off the line. I had flowmaster 40's and were too loud in my opionion, the interior droning sound was too much on the highway. Now I have Magnaflows, much less interior noise and still sounds way cool when you punch it, a bit more expensive though. Not sure how the 50's sund but they are supposed to control interior noise better.