Sounds like a great idea. Thanks for reporting the impact it had on your temperatures which is quite considerable. How exactly did you place these cable ties, i.e. did you thread them through the exposed fins of the heat sink, or did you wrap them around the entire GPU? Also, I assume you are blowing air into the GPU (from above downwards), i.e. in the opposite direction of a normal case's air flow which typically pulls in air at the lower front and exhausts them at the top and top rear - is that right? I wonder if it would be better to change the fan's air direction so it pulls air through the GPU (i.e. aligned with the direction of the rest of the case's air flow, moving from bottom towards the top of the case, thus reducing turbulence) - though I doubt it would be easy, as this would require a very tight fit on the GPU.