http://www.digitaltrends.com/computing/why-your-next-laptop-should-have-a-quad-core-processor/
These days quad-cores outperform dual cores even in single-thread scenarios.
And if performance isn't a factor for you, why not just go for the MacBook? The MacBook Pro, especially the 15'', is for users who need more performance. The 13'' is kind of a funny duck because it's a "Pro" device but it gets lower specs because of its form factor. In the past, that made the 13'' a "Pro" device with a consumer focus...
In my opinion (and doubtless Apple disagrees when you consider the Pro iPads), the 13'' MBP should go away or become a large MacBook, rather than an underpowered MacBook Pro.
But really all I'm saying is, if performance is something that matters to you, quad core is the way to go.