Hi Moriah
I am along time Mac user and use VRay for the same use cases as you.
IMHO if Vray rendering is your specific reason for switching, I would stay on Windows.
Rendering speeds are no different between platforms BUT there is a difference with GPU rendering.
Due to the ongoing issues between Apple and Nvidia, CUDA GPU rendering is currently not supported on MacOS under Vray Next (as Vray ONLY uses GPU accelerated rendering on Nvidia cards) as there are no official Nvidia drivers available for MacOS under Mojave for current cards.
You see my posts on the issue here.
However, with the rise of cloud rendering services (I use the new Chaos Cloud service) there is an argument that local rendering capability becomes less essential, apart for smaller, lower quality look development and scene development.
If it isn’t your specific reason for switching and are looking at a wider change to your workflow, thats different discussion.
I hope this helps.
Cheers
Rob