In my experience, tuna of all sorts bite best in choppy conditions, especially when trolling. But, I wouldn't want to drift fish in those conditions a sea anchor or bottom anchor would be necessary to stop the boat from rolling excessively. That is exactly where seakeepers would come in handy.
Great comments above.
My line of demarcation is 7 footers but then again for me that's pushing it. It becomes a truthful analysis of your own ability to maintain balance. If your a young buck, say under 65, it should be doable. On the American Angler a few weeks ago (weather report said 6-8) and got stuck in 10-? footers. Got broad side to a big'n which almost dumped everyone on the port side of the gally to the starboard side. No injuries but we all got tuned up with that event.
However ,,,after a certain length of time common sense analysis of the sea state becomes secondary , I just want to go fishing....