yeah my set-up is a 16v.  i have a modified air-box with a K&N drop-in filter.  so it's basically an open intake.  stock exaust manifold...but wanting the header.  and the cat back.  i can say with just this my 2-door MOVES.  that's with 235/75/15 BFG-A/T's.
after i put on the larger tires i really lost some top end.  it was alot harder to achieve and maintain 70MPH.  with just the cat back, if i don't watch it i'll catch myself doing 85+MPH without breaking a sweat.
i just wanted to say i'm very impressed with this product. and let everyone else that may be "thinking" about getting it, know it's a worthy buy.