Kalamabama,
I think there is more to the fish playing equation than just the pound test of the line. Assuming you're going to play the fish on a fishing rod, then the basic lifting power of the rod may be more of a limiting factor than the breaking strength of the line you are using. Let me illustrate with an example.
None of my single handed fly rods can break an 8# Maxima leader except by a "straight line pull." That is, when the rods are bent in a curve, as when I'm playing a fish, I cannot break that 8# leader. Every rod has a lifting strength that can be tested by tying the rod tip to a weight and seeing how much weight the rod will lift off the ground. For example, the most popular Tarpon rods have a lifting power of about 10 to 12 pounds, and these rods are used to play and land fish of well over 100 pounds. And they can do it well withing the one minute per pound of fish rule of thumb.
Knowing the lifting power of my fly rods, I usually use 8# Maxima for my leader tippets, and land steelhead of all sizes, including fish over 20 pounds, well within the one minute per pound. However, on some rivers, where the steelhead make notoriously viscious strikes, I've had to use heavier leader, not to play the fish, but to keep them from breaking off on the strike.
Some will think I'm using excessively light leader material, and that may be true in their experience. But I know for a fact that you cannot pull any harder on a fish than the lifting power of your rod allows - unless you straigten the rod and make a straight line pull using only the strength of the line to yard in the fish. And experience has taught me that by pulling against a fish as hard as my rod allows, I can land most steelhead in 5 to 10 minutes. A lot of anglers, especially novices, don't seem to realize just how hard you can pull against a fish. Most rods have a lot of flex in them, and even 5 or 6 pounds of lifting power exerts a lot of force against a fish.
The only advantage I can see with using 20 or 30 pound test line on a drift fishing rod is that you can use old line that's been exposed to sunlight (making it more like 10 pound test), you don't have to worry about minor nicks and abrasions on the rocks, and you can use a straight line pull to yard in snagged fish. It's also handy if you're fishing for large Kings. But I think the heavy line has a lot of disadvantages too. It has a lot of drag through the water and gives an angler less feel of what's going on with his terminal gear and takes more lead to make an effective drift at any flow level.
My main point is that it's prudent to use heavy enough line to fully utilize your rod's inherent lifting power. Any heavier line just gives you insurance against abrasion and the opportunity to make a straight line pull, if that's how you wish to land a fish.
Sincerely,
Salmo g.