maxwolfie,
500Ω and 20kΩ VRs are fine for vGPU and vMEM mods respectively.

Infact, we are not setting the 50kΩ VR in the vMEM mod to anywhere near 600Ω at all. We're using the 50kΩ VR to set the whole circuit to ~600Ω. The catch with the high rated VRs is that the added VR and the preinstalled SMD resistors are installed in parallel thus resulting in a bit different combined resistance than either components separately.