Well from what I have read before and can remember the 170 will be better. The cooler the engine the more power you will get. I did read to cool is not good either but above 170 is OK. As far as the differance between the two I don't know how noticeable it will be. Plus how close are they going to be to that temp.. I would think they have a +- factor. I would go with the 170 and reprogram the computer for it.