Many years ago I had two rods of the same make and model, and both 9-footers; one a 4-weight and the other a 7-weight. They were also kept in the same type of aluminum tubes so, of course, early one morning, I grabbed the wrong one. I was planning to fish for sea-run cutthroat and the only reels I brought were loaded with 4-weght lines and, naturally, the rod I brought along was the 7-weight. For me, the great surprise was that I was able to cast at all, albeit with considerable difficulty. It was necessary to get a lot more line into the air to even begin to load the heavier rod and required a lot more room for the back cast and much more effort and attention to keep from slapping the water behind and killing the cast. It was not an experience I would seek to duplicate.