Better gaming PC: A10 5800K w/ Radeon HD 6670 vs. i5 3450 w/ GTX 560

the i5 with gtx560 is far better. both the cpu and gpu are far more powerful.

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 560Ti

5800K 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.

What abou the crossfire the 5800k have with the 6670?

Yeah, AMD dual graphics mode. That's what the benchmark I posted is.