Have you used the DRAM timing tool(s) to get an idea of what your values could be with that memory? There could be a difference in some applications having faster RAM, but it's not like it's going to be some crazy big jump in performance. Most people do this out of the interest of doing it as an exercise more so than the actual performance gains of increasing their lowest 1% performance, etc, type stuff. Will it lower the life span? Sure, heat does that to everything ultimately, but you'll upgrade long before it's probably an issue unless you fry the RAM completely. If it's not stable it will cause more problems than not, so before you chase a specific number, worry about whatever you can get to that is stable.
Very best,