I don't think running at rated power (M.P. & RPM) is going to be an issue - but whenever one can reduce the TIME AT POWER it's generally beneficial to engine life.
Bearing loads are dependent on using the correct RPM for each MP - my old boss told me of an R-1820 operator who liked to take off at rated RPM but reduced MP - and his master rod bearing life suffered as a result.
Individual engine models have their own quirks, though, and staying with the builder's recommendation is the best advice.