My experience playing the D series Kanile'a tenors in the Kaneohe store is that the volume is INSANE. I felt like the guy in the old Maxell XLII cassette ads. Blew my hair BACK, son, no kidding.
Now, was that the D-shaped sound hole, the bracing, the strings, or what? Probably all of it. But yeah, very easily FELT louder than anything else I played in the shop. Kaimana Souza mentioned informally that he's thinking that these will be the year's bestsellers for Kanile'a, so I guess we'll see.
(And really, for me, the appeal is as much how nicely the D series shows off the wood on the top as anything else. Also, the side sound port is dynamite, and not all the models I played had one. Me, I've already told them that they need to standardize on these, as Chuck Moore has.

)
In general, for busking, I'd be more inclined to be thinking about resonators for volume as the wild card, rather than the location and shape of the sound hole. This is something that
@Yukio can tell you about, as a busker who is typically in areas that don't allow amplification, using a Mya-Moe resonator. Sounds loud to me over YouTube, but he can tell you the rest! Calling you,
@Yukio!