I might be a bit slow but I just realised that old intel cpu fan (4 wire) is very good for speed regulation if wired correctly. This must be the best fan for filament cooling? 70mm is a bit on the large side but boy it got some good performance!
https://drive.google.com/file/d/0B7kgdYk7GVumQkItaTJEZmhwcTA/edit?usp=sharing