I use 8lb for salmon on my leader and for my hook length below the swivel when prawning or worm and been successful many times. But I do know what you mean by using heavier lines for salmon but is that not because it's fast boulder laden rivers? That get snagged up more on. A ten pound fish isn't going to snap a rod or line if the drag system is set properly, it will if you try and pick it up out of the water so it shows the pressure a fish puts on isn't the same as the test curve or breaking strain whilst under water, I fish the moy and mourne for salmon, plenty of monsters in them aswel
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