[Steve Tinker]

I think particlewave's opinion is not quite 100% correct - it all depends on how good the original header design is & where you want the power delivery. If we are talking specifically Porsche M96, I'm sure the engineers put a lot of design effort into the final product, however initial fabrication / material costs, spacing & engine "drivability" all came into consideration way back in 1995.
My own experience with the Topspeed headers are mixed. They have been on the car since 2010 with no problems.

1) Running just the headers with the standard exhaust system, the sound is definitely different, especially above 4,000 rpm.
2) The torque spread has moved up the rev range about 500 rpm (probably due to the larger diameter), not a problem with my 3.2 S engine, but maybe it would with a 2.5 base. I measured each exhaust pipe - they are equal length, the original is not.
3) The fit was OK, but in hindsight I would enlarge the bolt holes for easier fitment. I also had to clean off internal weld to match the manifold gasket - a laborious job....
4) They don't tell you but you cannot fit the plastic undertray with the headers fitted.
5) Mine does not have that cheap looking crimped collector, which may negate any (?) power gain.