who makes the best quality headers with the most significant gains?

Crawfords. They are the most expensive, but you get what you pay for.

Lou

where can i buy these headers from?

http://crawfordzcar.com/

the crawford headers are nice for the hp however they are a pain in the rear to install...

If you want a nice well built header and dont' cost too much... the DC stainless steel headers are nice... They are going for about 600...

Street Image - 350z and G35 Specialists
2003 350z Enthusiast Chrome Silver

I just got a hold of the Pro-1 headers this week (they will be installed Monday - look for pics and a write up soon) - they are basically Fujitsubo headers made for a LHD car...they are definitely nice pieces... I will post pics as soon as possible...

2003.5 BS coupe 5AT
Clear Corners, Alum. Pedals, Pro-1 Intake, Resonated Test Pipes, UR Pulley, CF Engine Cover, GReddy EVO II, Kinetix Plenum, Hotchkis Sways

what was the install like and how much did you pay?

I've seen pics of both, totally different collector design and pipe routing, the pro-1's are copies of the Top speed headers which are a copy of the Dc Sport header.

Crawfords are the best because they hit fundamental elements of proper header design, this costs money to R&D and requires more time consuming construction techniques. Next up are the Nismo headers, which you can buy BRM copies of for $650 in mild steel or $795. Headers really do fit the saying you get what you pay for on these cars.