You could just square your quantity before applying the 1.5 factor. Instead of "Our shuttle is safe up to 150% of the required speed!" design for "safe up to 15

You could just square your quantity before applying the 1.5 factor. Instead of "Our shuttle is safe up to 150% of the required speed!" design for "safe up to 150% of the required kinetic energy (1/2 m v^2)". Then you only need to design up to sqrt(1.5) = 123% of the required speed. (My point is that the scaling of the importance of quantities is arbitrary so a single safety factor doesn't make sense to be applied to every quantity.)