Depends how far down you are going, but I would imagine 4th would be fine if you can handle it. There is nothing wrong with 3rd though, just be sure to rev match.
Others: what is this loss of traction you speak of??? Ride the clutch much?
I think the loss of traction they are referring to would be the skidding you would experience if you don't rev match that shift. And 6 - 3 would take a significant rev match. Agreed, 6 - 4 is a better choice IMO.