Cake Flour 5 years past its "Best by" date

I've got an unopened carton of Swan's Cake Flour with a "best by" date of June 2013. Is it usable? I am not worried about food safety as the box is completely sealed and I believe the flour is inside a vacuum sealed bag inside, similar to how cereal is packed. I am just that the flour would in some way be inferior in taste or chemical properties.