I would not use Fluro for spinning, just yesterday I went over to buy some of this stuff. They had what they claimed to be the softest Fluro in the world, I did not look at the 8lb stuff the the 20lb Fluro was still far to stiff to spin with.
What is the Brand of fluro you use to spin?
I use Berkeley (picture in my post above) 8Lbs and sometimes 12lbs. On a 7' Medium action fast tip rod with lures from 1/3 to 1/2 (sometimes almost 1 ounce with sinker and all) without any problems.
I almost always fish from a boat. When fishing from a boat you are not looking for long lasts as you cast parallel to the shore. I also keep the wind behind me. maybe that's why it seems to work fine for me. People I fish with also use fluorocarbon lines on spinning reels. I have also seen flurocarbon lines which are as soft as monofilament. when florocarbon lines initially were introduced they were stiff. But, recent changes in compound has made them acceptably softer.
I also use a swivel with a leader 18 inches long even on worms. To avoid any twisting. Maybe this is what I was missing in the information. I just called my buddy. The 15Lbs line he uses is Seaguar Invizx. He has no problem as long as he uses a swivel.
But, this is fishing. What works for me may not work for you.
I am just thrilled at picking up all the 'desi' tricks on this forum. In the last week I have seen many things which I want to try here.