i successfully installed a 2003-2005 header onto my 2007 R6. pros: gets rid of cat converter power gains (tune w/ new numbers coming, i have a baseline of 106 stock) -- supposed to be the same power gains as a full system cuts around 8 pounds off the bike based on my scale cons: some fabrication needed (see below) not the full weight savings as a real full system what this involves-- purchase a 2"ID to 1.75"OD coupler from auto parts store ($2.00) go to exhaust shop and have them expand the 2" end out to fit over the tip of the header (cost 5 dollars) bore out the exhaust flanges to 3/8." I had to take a dremel and oblong the holes a little as well. mount up the header, put the smaller end into your slipon and attach the coupler/slipon unit to the header. the mounting point of the slipon to the rearset is about 3-4" off. cut the tip off the header until you get to the point of where you can mount the slipon. don't overcut here, so if you need to cut more than once thats fine... once youre all done with getting it to fit correctly, go back to the exhaust shop and have them weld it together for you (or a friend), this cost was around 20 dollars. so with the cost of the header my total cost was 80 dollars to do this vs 1000 plus for a legit full system. Even if there is a 3 hp increase it will be worth the money. Based on what other people have posted after they do this I expect at least a 3-5hp increase when all said and done. ill post up pics when i get my phone synced tonight. sound db has increased a lot, and the tone sounds really good, not raspy or annoying at all. i have the stock slipon connected right now and the idle is the same but any throttle input and you can tell there is something different behind the fairings...