What is more important spending your time building a culture of performance or hiring top performers?  

This dilemma is often faced by executives and reminds me of the nature vs. nurture debate.  But as often the case in such dualities, the solution is in the middle.  Historically speaking we have been pushing the selection using assessment tools to uncover the best performers (nature) while most organizations spend more on training (nurture) than recruiting (18.3% vs. 13.6% of HR budget).  

A good analogy to consider in this regard comes from genetics, and specifically epigenetics, or how your environment (culture) will enable you to express the gene (nature).  You need the gene (talent) to achieve the performance, BUT you need  the environment (culture) to turn it on.  

In short you will need both aspects.