J-Moe, I don't know. I like the way 4 lbs line casts on my spinning set up. I seem to get more bites with 4 lbs mono. I used to have fluoro, but it seemed to twist up too bad for me.
I've caught may bluegillon 6 lb hi-vis line, but the 4 lb. seems out out perform it every time.
I actually seemed to have more success using 4 lb. mono tippets than 6 lb. fluorocarbon tippets, but I can't quantify that.
I tried the 6 lb. p-line on my spinning gear and it twisted so bad I had to cut it off after 2 fishing trips. I bought some other pure fluorocarbon but haven't tried it yet.