M20B25 - Which headers work well, Which dont?

[Z2TT]

Hello.

I have a E30 325i, so far to increase performance I have put a performance chip in. In other areas from my research M20B25 doesn't seem to have big room for improvement, I understand exhaust is pretty free flowing, I was thinking to change the cat converter with highflow as Wikipedia seems to say non cat versions make 5kw more??, is this truth or only on paper.

My next step is to put a better header on. Which diameters and lengths work the best?

Is the Alpina one good and is there any headers that replicate the diameters and lengths as the Alpine one?

Street driven car, so I do not want to lose low end power that M20 lacks to begin with.

Thanks.

[Speedtouch]

The BTB was shown to give a gain of around 15bhp on bss325i's standard 325i Sport:

http://www.e30zone.net/e30zonewiki/index.php/Exhaust

[reggid]

BTB and racing dynamics (original) ones work well.