I've caught a total of 13 tunas, but I caught them all with a performance plus. I know somebody who caught a dicy tuna with grade F and a basic... shortly after I caught my first dicy. We've been aiming for 'Inos ever since. Still haven't caught any...
Anyway, I think that the answer to your question would be, in my book, performance plus with grade A bait. Although it is expensive, it makes reeling in those tough buggers a breeze once you get used to it. Once I got THREE tunas in a single bucket. Icy, and two dicys. So, good luck getting those tunas!