the i5/560Ti setup is monumentally better. It will kick the absolute crap out of the other system in every possible regard. Here are some benchmarks to show you. 3Dmark11 is one of the best benchmarks to judge a PC's gaming performance.i5 3450 with 560Ti5800K with 6670
If you compare the graphs, or scroll down and look at the detailed scores, you will see the i5 setup scores over 3 times as high as the 5800K setup does. Of course, the power comes at a premium price, and the i5 setup will cost you at least $150-$200 more.