Gamma 4# Polyflex or Panfish either one breaks at 8.5 pounds actual and has beated muskies to 38 and 40 inches and largemouths to 22" for me. Gamma Fluorocarbon Edge 4# breaks at actual 7#.
I have been using Polyflex 4# as my main line for years and cannot say enough good, except that I switch to Gamma ESP Ice 4# in early and late open cold water because it is softer and smaller diameter, but it also breaks at about the same as 2# Panfish which is right at a true 4#.
Furthermore Gamma corp is easy to deal with; so I buy my lines direct from the manufacturer online.
Disclaimer: I have zero financial interest or connection beyond simply being a satisfied customer.