The GFCI will remain fine, as long as you have wired the circuit with AWG specified for that circuit, and distance.
Example: A GFCI wire with 14 AWG for a 200 foot run will not (In my opinion) protect the loads of that circuit properly do to voltage drop. In theory: The Electrons loose energy by giving it up to resistance--in the form of heat.
In theory: The more loads there are, the less voltage drop.
This is open for debate!
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