Hi Brad,
On my last trip out on Oahu i tried to see just how far you could push PE8 line. There were two occasions when its limits were met; mostly because i didnt bring my heavy gear!
The first fish that broke the mainline struck the plug about 10m away from the boat and looked to be about 30kilos or so. The fish took out about 8-10m of line and i decided to clamp the spool with my left hand to see if it was possible to stop the fish with PE8. The fish stopped, but the line quickly broke right after the fish stopped. We were fishing in about 75ft of water, so the fish was nowhere near the bottom. The line appeared to have broken a meter or two above my knot (color coded line). I am confident that the line wouldn't have broken with PE10.
The second fish was a pretty similar situation. Deep water and it it was the end of the day. A good fish struck, and i really didnt want to crank in too much line, so i clamped the spool and tried to dead stop it near the boat. Again the line busted well before the fish reached the bottom.
On a previous trip i hooked a good fish in shallower water. We were hammering on it with the boat moving at a pretty quick speed to get the fish out of the reef. Under such high strain of the boat, the line busted with the reel clamped down near lock.
All three times was clamping the spool with a Van Staal275 and PE8 line tied to 200lb leader with an FG knot. The other times i have used heavier line PE10-PE12, i have never had an issue with line snapping.
That being said; i am also fully confident that i would've landed those fish on PE8 with a little more patience. If you go looking to break something, you're probably gonna break it, haha! Sometimes you just gotta test things to their limits to know how to distribute your confidence.