on a track car a 5 or 6 angle cut makes sense but on a street car it makes little sense to do this. a 5 angle cut although making a much smoother air flow transition around the valve will make for a less robust seat and shorten the life of the valve. the horsepower is increased with a 5 cut job but the seat is reduced shortening the life.

if you are going to go through all that trouble of a full valve job limit your self to a 3 angle cut not a 5 or 6 for your turbo street ride.