Finally decided (after posting on the forum for advice) that a GYTR Aluminium exhaust on my WR450 was the best combination of price / performance / looks. I was not dissapointed, its a really well made bit of kit. While its not easy to figure out real performance gains as its so subjective (and small) I was looking for more low end grunt and I seem to have found it. I have not had to rejet either (still running a 165 main) as there is no hesitation throughout the rev range - and if anyhting the plug colour is still telling me its too rich, which was surprising. If the plug colour is showing its still running rich but it feels strong should i leave it be or try leaning it out on a 162 main? It is LOUD though!