I bought a Stage 3 filter and PC3 for my 2007 XTR. The O2 sensor had been removed and an eliminator fitted. The dyno shop could not get the PC3 to build a usable map because they said the dyno could not "handle" the fact there was no O2 sensor. It seems some of the 2007 ECU's have a fault in that they run rich and I appear to have one of those. VERY long story made short......I have ended up with the stage 3 filter, and everything else as standard and the bike runs very well indeed. Just a (very) teeny bit of surging at low speed, plenty of extra hp everywhere, getting about 20K's per litre as average. I fitted some Staintunes last week and now have even less surging, even more hp, and (not totally proven yet) better fuel consumption. Here is my 02c of analysis.....by chance I suspect the over-rich ECU has mated quite nicely with the Stage 3 and Staintunes. I spoke to Kev several times whilst I was going through this process and his simple words of wisdom were....if you are getting less than 18K's per litre bike is too rich, if you are getting more than 22K's per litre bike is too lean. How easy is that? I'm not trying to say that anyone should do this or do that, this is just my story.