After some very, very quick testing -- this fix is the real deal.
However, this fix ships with GI turned completely off (set to 0). Playing around with it in-game, I wouldn't recommend this, as GI does do something (surprising, given that I had no idea it was even in the game until everyone found out it was tanking performance).
Leaving it set to 16 (i.e. the lowest setting that's non-zero) seems to work the best. You still get GI, but it won't demolish the framerate (and, honestly, at 16 it looks about the same as the default 128).
To test this yourself, head to a grassy field (like where you start after the prologue/tutorial level). Turning GI off removes most of the lighting on the grass, making it appear dark and partially unlit. Setting GI to 16 restores the "proper" lighting, while still giving you better performance.
On my 1080, setting the GI to 16 rather than default 128 saves me about 15-20% GPU utilization at 1080p. Pretty nuts.