I know...what can I say. It seems that the smaller 15% reduction pulley delivers better consistant power runs and strip runs. However having driven a 17% on the road and my 15% on the road I have to say the 17 seems to have the edge in mid/high rpm range @ higher speeds. I am assuming (as stated before) that this is because the 17% can eventually get cool enough at higher speeds to start delivering the extra power it can through generating higher boost levels). I'm not mechanic but if you don't have an intercooler don't go to 17% IMO as the stock one really really struggles (I should know
) even on the 11 and 15% pulleys available on the market so on a 17% is really will be cooking brakfast in seconds of firing up!