According to the Microsoft website. "At a minimum, the requirements for graphics cards to be used with RemoteFX are: DirectX 11.0 or later, WDDM 1.2 driver or later"
So basically, any card produced in the past few years should work fine for testing.
https://blogs.technet.microsoft.com/enterprisemobility/2013/11/05/gpu-requirements-for-remotefx-on-windows-server-2012-r2/