A quote from Brian Litz: applied ballistics
"On the other side, over spinning a bullet is a bit of a myth. So if your barrel twist rate is far faster than recommended, you only need to make sure you account for the added spin drift"
I can assure you there is a reason 6ppc guys are on the ragged edge of stability. For the purpose of long range hunting I will take a sg of 1.7 over 1.3 any day but I do not get hung up on it. If going custom you might as well do it right.