I gotta chime in... Never tried or heard the Dynomax, but I'm a HUGE fan of the Cherry Bomb Vortex. I had the Flowmaster Super40, liked the sound, hated the performance. Switched to the CB Vortex... MUCH more tame on the sound level, yet still gets attention. More spaghetti than ricey, IMO. HP and MPG back up to where they "should" be. I hit 350 miles (range) on city/hwy last week... could NEVER come close to that with the Flowmaster (more like 280ish).
But... not an apples to apples comparison.. I understand. (single in/out muffler)

---JIM---