As long as you're using a longer moderate action rod, you'll be ok. Longer rods act like a shock absorber and do more of the work, perfectly fine in some cases. Now if you were using a shorter rod, then you're asking the line to do more of the work which will lead to a break-off. You could definitely get away running 2lb on a 7'+ moderate or moderate fast rod. I purposely fish steelhead that way when the water is low, slow, and gin clear. I've caught fish to 6lb with my 7'6" noodle using 4lb Ultragreen.