I am sure that others can weigh in better than I, but my understanding is that if the same amount of force is applied to different lengthed/ same weight rods, each 6"= approximately 5' of distance. I had a 10' 5# that I found tiring over the course of the day, so I now just use a 9' and enjoy the casting process more. As for the actual weight rating of a rod is anyone's guess as the action is a large concern. I think at about 7# I can really notice a fatigue difference. And in fact, because of that, I have gone to shorter softer rods (discontinued Scott 8'8" HPs) in 8#,9#, and 11# which I like more. The softer the rod, I believe the more work the rod will do, and subsequently the less work I have to do to get the line out. But I am not a burly guy, so I think about these things. Again, just my $0.02, and it may not be worth even that.