What should I purchase first S&B cai or Magnaflow muffler
 

2007 XLT 4.6 2wd. Whichever I purchase first, the other will be purchase months later. Which one work best without the other? I'll learning toward the magnaflow muffler with dual exhaust. BY reading the forum it seem 18" is the prefer choice by most with behind the wheel exit pipe. (No cab noise).

Either would give about the same performance boost.

I'd do the mufflers first, because you can hear them working.