Since the ReLive driver update I have tried every Radeon driver available, but borderless window freesync is just not working on my machine.
The games that I have tested include Watch Dogs 2 and CS:GO. Freesync is working for both games in normal fullscreen, so it is definitely an issue with borderless.
Radeon Driver: v17.3.1
OS: Windows 7 64 bit
CPU: Intel i7-870
Graphics Card: Sapphire RX 470 4GB OC
MB: ASRock P55 Deluxe3
RAM: 10GB DDR3 (Corsair XMS3)