This weight forward 5 Wt  Amplitude Smooth Infinity Camo Fly Line by Scientific Anglers is perfect for 4 and 5 weight rods.  You can either "overline" your 4 weight or match your 5 weight perfectly.  The Amplitude Smooth series of lines are the highest-performance smooth fly lines in the world. With up to five times less drag and eight times the durability of traditional lines, this will change the way you look at fly line performance.