You can always fish a disk drag reel on its lightest setting. I have numerous Ross Gunnison reels that have a nice disk drag but I nearly always have the reels set very lightly, only to prevent overruns of the spool. I do however fish with a Tibor Gulfstream that would stop a truck if necessary. It is always set light and then tightened up as necessary. The key to catching a truly "big" fish is to allow it to run itself into fatigue by pulling on the light setting, absorbing the weight of the line that's out, and the friction of the guides on the rod. A sailfish will pull out several hundred yards of backing and jump numerous times before it tires but to get one in you don't need a heavy drag, just patience and then the "know how" to revive and release it successfully.