With engine freeze since 2007, the emphasis on Formula 1 diverted more into aerodynamics in 2007, 2008. Then diffuser since 2009~2011. And 2012 are the tires, and how to make the tire works for you the longer shall win. Which also factor in how well the drivers are able to manage different tires in different tracks, and now that skill set is more important than before.
Overall engine performance in recent F1 is less a differentiater, its more about aerodynamics, suspension and how will these make tires work the best.