The only thing either of them has been able to provide was some charts that show how much stronger theirs is compared to the "Leading competitor". It seems quite paradoxical though because Neapco must be Spicer's leading competitor and vice versa, yet they both claim to be multiple times stronger than their leading competitor.
I can shed some light on this based on my experience in that world (design engineering in the automotive and power sports industries.) Marketing folks like comparisons, but lawyers don’t. So, they compromise. The vagueness (not naming the competitors and not giving test specifics) satisfies the lawyers, and the marketing folks don’t really care because they don’t understand the tests and assume the general public wouldn’t either. They’ll not release that information because the lawyers want the vagueness to keep from getting sued. The truth in advertising rules only require you to have test data to back up your claims, but that data doesn’t have to be made public, and keeping it private makes it difficult for a competitor to prove you wrong. They’d have to sue, but since they are not specifically named as the competitor, and there are no details regarding the tests or the results, that (suing) doesn’t make sense to them. It’s like trying to nail Jell-O to the wall.
Also, Spicer only shows "fatigue cycles to failure" but they don't explain what that means. Neapco shows fatigue cycles to failure but they also have a graph with "Ulitmate strength" in Newton-metres.
Here’s how I would have tested these if I was the design engineer. For the fatigue cycles to failure I’d run the u-joints in a very stout pair of yolks on a dynamometer at a constant load (torque) and fixed deflection angle and count the revolutions until the joint fails. As the joint makes a revolution, the loads on it change direction as it accelerates and decelerates, so each revolution is a load cycle. There are a lot of details that need to be worked out, and that’s part of the beauty of the vagueness the lawyers like. How do you replicate something that can’t be replicated?
As for the ultimate strength testing, I’d put the joint in another very stout pair of yolks, and then I’d run it in a torque testing machine (Instron makes them), where it would be twisted to failure, while recording torque and angular deflection. By looking at the torque/deflection curve, you can see the point of failure clearly and determine the torque at that point, which is the ultimate strength.