I have to respectfully disagree with this. I double clutch nearly every downshift unless I'm going as far as 4-3-2 where there simply isn't time if the brakes are working properly. Syncros or not, matching the RPM in neutral is much smoother for me and I'm much less likley to upset the car. One less thing to think about as you enter the corner. The only time I won't double clutch is for an ugly 2-1 shift while autocrossing, mainly because the car is going to be upset a little anyway. Fortunately, I haven't ever had to do that on the track.