I've never done bluefin, but I've got more than a few yellowfin to #38 (I'm not sure I want a #50 pounder
), pacific sails, and yellowtail under the old belt. Not braggin', you want to catch those fish, all you have to do is go where they are. Anyway, my standard class tippet is #15 pound Berkley Big Game, which seems to break around #17 to #22 pounds
I only use twenty if I'm going straight to the fly with it. Hook up your heaviest rod to a fish scale and have a buddy read the pounds while you put as much pressure as you dare. Not the same as fishing because the scale doesn't fight back, but you will be shocked at how little pressure you are willing to put on the rod. #15 is more than strong enough, and when you need to you can easily point at the fish and give a tug and both of you are done with each other.
Industry folks will tell you to assume #30 pound breakage on your fline, regardless of weight (we're talking 8 weight and above here). Has to do with core, not the plastic around the core.
Go get 'em and be "safe not silly" as my Mom used to say on Friday nights when I was a young buck