FX-4170 is just a pre-overclocked version of FX-4100 for increased price. You can overclock the FX-4100 to 4.2GHz yourself without increasing voltages or cooling power and it will provide equal performance just like the FX-4170.
Again, buying FX-6200 is just a waste of money as it is just a pre-overclocked version of the FX-6100 and is a little bit more costlier.