I am not qualified to give an authoritative answer to your several questions. My thoughts are that you should aim for "full coverage" unless instructed otherwise. "Full coverage" is defined as being at least 98% denting of the surface. It is recognised that it is very difficult to obtain accurate measurements of coverage above 98%. 200% coverage can be regarded as peening for twice the time required to achieve "full coverage". Personally I feel that 600% coverage is excessive and runs the danger of overpeening the component. Perhaps you could amplify what you mean by "peening to intensity" - it is not a phrase that I am familiar with.
