A 512x512 haldclut corresponds to a 64x64x64 cube while a 1728x1728 haldclut corresponds to 144x144x144 cube. The interpolation calculation will be more accurate in the second case.
If I remember well the rawtherapee halcluts are 16 bits instead of 8, which provides also more accurate values.
To be honest, I’m not able to see any difference in the result.
GMIC team considers that a 48x48x48 cube is enough to be accurate. That’s the size of the compressed clut.
I cannot answer really. Can you see the difference ?