If the E85 tune is correct you won't have any trouble with your 02's. I've been running a full E85 tune and headers for over a year, zero problems and my 02's still look brand new (just checked them last week).
Because we don't want to take the risk of shitty fitment or headers that rust after a few years. I had Hooker's on an old LS1 from the previous owner and ended up with an exhaust leak on the manifold itself. Never again.
I agree. Headers is one of those jobs I want to do once and not think about it again.
Not sure about the bottleneck... As a whole the factory exhaust SYSTEM (ie...headers to mufflers) flow pretty well. As I understand it, a majority of the restriction lies with the factory cats...which is why some folks just do cat deletes But the headers are worth a few more and certainly help for the future, so I am doing long tubes and the magnaflow tru-x from CJ pony parts and leaving my factory active exhaust.
If ever going FI you would not want to do the step down design of the Pypes. If staying NA it shouldn't matter.
Bottleneck elimination is where the mid pipes on your headers remain a full 3" instead of bottlenecking to the size of the factory system or some aftermarket cat-backs at the connection point...
