Not sure when we started doing this, but we tend to over-line (go up one line weight) on our 4-Wt and 5-Wt fly rods. I think we did this by accident when we used whatever fly line we had at the time we picked up a new fly reel.
So far, have been good with the casting results by going up a weight. That said, was not aware of a debate about this, until I saw an article online by Field and Stream – “Is Over-Lining Fly Rods Good or Bad?”
For the most part, would agree with Field and Stream that there are no set rules. Would go on to say, “whatever works best for you”!