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I had 5100 on my 2014 FX4, on my 2018 I went with 6112 and 5160. Feel wise the 6112 feel a little stiffer than the 5100 on the front. The 5160 in the rear are the same as regular 5100 with just more oil. If you just do occasional off road and mostly street 5100 are great. My choice to go to the 6112/5160 was purely based on the looks and upgraded front springs as I am thinking of going to a heavier front bumper.
4600 if you do not plan to raise the front. I just replaced oem fx4 shocks with 4600 and love it. Truck feels and handles much better. Plus 4600 are inexpensive, got them (front and rear) delivered from Amazon for $350.