The i7-3770s goes for $305 on Newegg and the i5-3570k goes for $219 so you could save about $90 by going for the i5-3570k and have a much better gaming CPU with an unlocked multiplier. The i7-3770s has a stock speed of 3.1ghz compared to the stock speed of 3.4ghz for the i5-3570k which can be further overclocked much higher.
The only advantage the i7-3770s has is Hyper threading which most all games do not take advantage of. So from a gaming standpoint the i5-3570k is the much better and less expensive option.