Major difference: V Pro is ATX, M Pro is MicroATX
One more SATA III port in the V Pro
Intel network controller in the V Pro (better than the Realtek in the M Pro)
USB3 internal headers in the V Pro
More USB2 rear ports in the V Pro
QuadGPU support in the V Pro
Onboard Bluetooth in the V Pro
Onboard Firewire in the V Pro
No PS/2 port in the V Pro