There is a substantial difference.
The 5100 is a shock that you would pair to a coil of your choice. In this process you will choose a ride height setting and then assemble them. This will determine the amount of lift you have and cannot be changed unless you take it back off your truck and disassemble.
The 6112/5160 is more of a complete kit. The coil will come with the front shock and will have adjustable height. This means you can install this on your truck, see what it looks like, and still move it up and down as desired. You will also have a remote hydro resivior that will give you better performance off-road (drive over hard bumps faster and feel it less, for example).