What is the rate of beneficial mutation in higher vertebrates?

That is an unanswerable question. Mutations are beneficial, neutral, or deleterious in relation to the environment. Is a paler moth or a darker one more likely to survive? That depends on where they rest and the background color. The classic example is Biston, the peppered moth, which became darker during the Industrial Revolution (soot-covered trees) and paler when the soot was cleaned up.