I use 75 yards of dacron as backing and then fill the rest of the spool with about 150 yds of Sufix Siege, which after a period of trying other lines proved to be the best casting line I could find. I use the 12 lb test smoke green for steelhead, but they do make a 20lb test for which would work for bigger salmon. I spool a 3.75" Kingpin Regency I have with Sufix Elite for trout and even pinks which I pair with a 7-weight fly rod I built into a float rod. I have never reached the backing on my centerpin and the dacron helps to avoid getting the line on top of it from getting settled into itself, making casting difficult. DO NOT USE BRAID. If braid gets tangled at the tip-top and you don't notice it before you cast, it can take the tip right off your rod. I also would not advise putting any line rated above your rod's capacity on any rod, centerpin or otherwise. You're asking for a snapped rod that way. As far as tiring out a fish that you plan on keeping there is no harm in that...but if you're planning on catching and releasing the fish then you should be able to get a larger fish muscled in quickly. You have to consider that float rods are long not just for proper drift/line taming considerations, but also so that they can provide some buffer and shock absorption properties not found in other styles of rods. This is especially true with centerpin rods and why you see them in lengths upwards of 15'. You should have no problem getting a 20lb king to the bank with 12lb rated line if you play the fish properly and let your rod absorb head shakes and don't clamp down on the spool when the fish wants to run a bit. Think about how you're holding the rod and make sure that it is positioned so that you're getting maximum shock absorption (tip up...never hold a float rod on a flat lateral line parallel to the ground). Oh and use your arm as an additional shock-absorbing extension of your rod and you should be fine.