I'm a bit late with a comment, but I've decided that I get the best results overlining most graphite rods at least one weight. There are exceptions (actually only one of 1 of 5 of my favorites suits me with the rated line weight, but it's a DT line on it now), but for most at least a 1/2 weight heavy line matches my casting style.
Sage Vantage 7'0" 3wt / WF4F line
Ross Essence FS 8'6" 3wt / Rio Grand (3 1/2 wt line) WF3F
Sage Graphite II 9'6" 8wt / WF9F
Ross FlyStik 7'11" 6wt / DT6F
StCroix RioSanto 9'0" 6wt / WF7F
For long distance casting I may switch to the rated line weight, but most of my fishing is short distance casting and a fair amount of roll casting is involved, so the heavier lines give me better results. Especially in the light (3wt) rods!
A 20-30' cast with a little wind and a 3wt line is pure folly in most cases.
The Ross Essence FS 8'6" 3wt is my newest rod and the initial fishing with a standard WF3F was not too difficult, but the Rio Grand line gave me a very noticable improvement in performance. Still need to try DT3F and WF4F on it.