I have run 2 different headers since I took off my stock manifold.
First was a QuickTime Completely equal length header.
Seemed to really let the engine breath along with sounding just like a DSM
Main problem was it was weak and leaked like mad
Second one is a Elcheapo off EBAY that Junior took a look at before I put it on. Thought the tubes were a bit small in diameter but I only have a 2.0 so it wouldn't hurt it to much? It is an EL Tri Y style so it has a completely different sound than the Quicktime. However it spooled in the 750 to 1000rpm range quicker than the QTP header
Here it is mounted to show it clears a stock WRX pan no problem. It came with crappy looking gaskets but I already had some stockers so I used them. Along with a 2" EBAY up pipe that I got separate.
Sorry I don't have more info on tube sizes at this point or any dyno sheets on the new header to prove a plus gain. It sound a lot different and spools way quicker, also both of these headers where feeding a old school FP Green on a 2.0 EJ207.
QTP Header made 405 WHP 22 or 24 psi @4500rpm as I can't remember it was so long ago? No dyno on new header yet.
Forgoy to add the new header let the Green hit 32 psi when the WG stuck. QTP 24psi was max it could make.