I've been fighting fish this year with the intent of finishing the deed quickly. I've yet to see backing though I've caught a number of fish that would have had me into backing in previous years. I have broken several off and subsequently moved from 12 to 16 to 20lb flouro. I agree with Sean in that given 100% knots and fresh tippet 10 or 12lb test is sufficient and we probably never apply more force than that with 9 or 10 wgt. rods. But if I want to avoid breaking fish off because of a deterioated tippet or a less than perfect knot 16 or 20 lb seems to be the way to go for the fishing I do.