After suggesting that "proper thinking should always lead to righteous deeds", you ask, "What is the word that describes the intellectual ability which produces only virtuous acts?". In the absence of well-defined terms and qualified circumstances, such an ability must be termed a fixation, a monomania. Ordinary humans never produce unmixed results; in the life of any real person, bad actions will be found among the good.
Less generally, the answer depends on what definitions are given. For example, taking proper to mean "suited or acceptable to the purpose or circumstances; fit, suitable", righteous to mean "justified morally", virtuous to mean "full of virtue (in accord with moral principles)", and moral to mean "conforming to a standard of right behaviour", it is a tautology that
proper thinking will lead to righteous deeds, and no intellectual ability is needed beyond that of being able to think properly. This may be termed as having the power of reason. For example, in a famous gardeners wikipedia article we find (emphasis added):
...the Age of Enlightenment (also known as the Age of Reason) ... was an era of scientific awakening with a strong belief in the power of reason as the primary source of legitimacy and authority.