It's not all about the clock speed. The 8350 doesn't have the architecture that the newest Intel CPU's have. The space between each transistor on the Intel chips is quite a bit smaller than the AMD chips, which means overall the CPU can do more in less time. Also, Intel's latest chips are hyper-threaded, meaning each core can handle two threads, whereas AMD's CPUs can only handle one. Then there are cache sizes, which allow the CPU to store memory on the chip itself for quick access.
Intel's chips are overall better. I would only get an AMD if you are on a strict and relatively low budget. If you want other sources, I recommend you look at CPU benchmarks to get a general idea of how CPUs compare to each other. It can be hard to look at just specs and say which is best, so benchmarks are the way to go.
Also, the 3570k benchmarks at about the same as the 4570k. If you can find a good deal for the 3570k, you might save some money that you can put somewhere else.