The 4670 is better than the 4570, it should cost a little bit more too...
About the FX 8 core CPU it all depends of what you are doing, the quad core intel as a better performance per core so in games or applications that use 4 threads or less it will provide better results, if you are using applications and games that use more than 4 threads the 8 core FX will catch up and in future games that are said are gonna use more threads the FX could provide better performance in the long run...but the FX consumes a little more power and will generate more heat too...it is suggested that you get an aftermarket CPU cooler for the FX and overclock it to match the intel performance.