Flying Crane
Sr. Grandmaster
I would absolutely put the spinning backfist into the list as a circular punch. I believe there are better and worse ways to root and rotate to deliver the power with it, not everyone does it the same. But when done well, it can be devastating. I practice the spinning backfist on a heavy bag regularly. It is very powerful.My primary empty hand training is in Wing Chun, a short-bridge, linear southern Chinese martial art but I have to agree with Crane and Jow Ga. Those long-bridge, circular punches properly executed generate a lot of power. Moreover, when it comes to how much useful damage a technique an do, I'm not sure how far I would trust a "StrikeMeter" reading. I've never used one, but from what I've seen, there are a lot more variables involved besides what a device like that might measure.
BTW when dealing with multiple attackers, even in a "linear style" like Wing Chun we often fall back on flailing fak-sau and man-sau strikes which have a long reach and a somewhat circular quality, and a similar whipping force augmented by body rotation. Heck even a standard karate/mma spinning backfist is similar in concept.
To sum it up, I wouldn't underestimate these circular, whipping long-bridge strikes when dealt by an experienced fighter!