Non-K CPUs are locked so overclocking is extremely limited, whether it's SB, IB, or Haswell.
What will make the difference here is what graphics card you pair with it. All else being the same, the i5 is the better choice, but if getting the i3 frees up money to get a better graphics card, in most games that would be the better choice. MMOs may be an exception, as they are often more CPU-bound.