The pro circuits are a low-mid pipe with a redline of around 8,800 rpm or so. If I was going to run a stock motor with a mid-top pipe. I would put a set of Paul turner high revs, original fmf gold series, or the fmf sst on it. The T5 is prety much a knock off of the original gold series pipes with less lower midrange pull. I dont know why they made the T6, its a little more useless than the T5. I would probably run the fmf fatty over the T6.