I suggest searching the Photoshop site for compatible GPUs. I know they have a list somewhere. As long as the GPU is compatible with Photoshop then Pixnub will work fine too. Pixnub just tells Photoshop to do things and all of the work is done by Photoshop using the same set of tools that you could use by hand in Photoshop.
@ Ricky Green
With Photoshop/Pixnub, All face detection is done by the GPU. Even if it doesn’t use much GPU power, it is still being done by the GPU. With an incompatible GPU, face detection will have issues. If you go into the Photoshop preferences under the performance section and uncheck “Use Graphics Processor” then you will find that Face Crop will not work and Face Detection in SPA and EZ Team Builder also won’t work. Face detection issues are almost always a GPU compatibility issue.