Q. What are the hardware requirements for a Hyper-V or Remote Desktop Services Host to take advantage of RemoteFX?

A. Microsoft provides a fairly detailed hardware requirements document for RemoteFX. This page also has scaling information for the amount of graphics memory you'll need on the server for different numbers of clients based on resolutions and number of monitors.

The basic, high level requirements are:

1. The processor must support Second-Layer Address Translation (SLAT). SLAT lets a processor maintain the shadow page tables that map physical memory to virtual machine memory, saving overhead on the hypervisor. For Intel processors, this feature is known as Extended Page Tables (EPT). For AMD, it's Nested Page Tables (NPT). Only newer processors, such as the Intel Nehalem-based processors, support this feature.
2. The graphics card's GPU must support DirectX 9.0c and DirectX10. If you have multiple GPUs, they must be the same card. If you want to use Live Migration or Quick Migration, the source and target nodes must have identical GPUs.
3. You must have at least 512MB of graphics memory.
4. Your graphics card must, at least, be in a PCI-Express x4 slot—ideally, it should be in an x16 slot.

Optionally, you can use an encoder card. The card is a dedicated piece of hardware to help in graphics rendering and enabling greater scalability.