I would not recommend kratom or any stimulant as a substitute for sleep. The best thing for your productivity is natural sleep. For the purposes of productivity enhancement, I think kratom and coffee are best consumed during a day as slowly as possible... if you feel yourself getting tired or distracted, take a sip.

I don't feel that kratom use hinders higher intellectual function in sub-opiating doses but this is difficult to measure.

There is only one good pharmaceutical solution for suppressing tiredness without other side effects: Modafinil. http://en.wikipedia.org/wiki/Modafinil This is an account of extreme Modafinil use and abuse. http://www.erowid.org/experiences/exp.php?ID=45423