We cant identify all the risks of an investment or portfolio. There are risks that we can identify but there are also unknown risks that we cant. So the total risk is unknown. Lets assume that SD is one of the known risks, which I believe it is. We will never know SD's percentage of total risk and that wouldnt be a static metric even if we did. So, to answer your question "what is the risk adjusted return", I have no idea neither do you. You can figure a SD adjusted return and call it risk and pitch that to clients because the average investor doesnt even know what SD is. Or better yet, put it into a model and really confuse them.
Cheers