@Saltgrass: I did run the whole of ASUS mobo disc, including USB 3 drivers.
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@Joe S: It's a ASUS Sabertooth 990FX mobo, support up to 8 USB 3. I connected my disk directly to to mobo USB 3, so it shouldn't be a problem with cables.
HOWEVER: I seem to have solved the problem. I deleted drivers manually, according to Windows Device Manager, resulting in a small catastrophe where my mouse wouldn't work, and my keyboard was more or less handicapped. I was about to give it all a big kick, but then I restored my Windows from an image and... guess what? Here I write, and the blasted Buffalo runs at 3.0.
End is well, all is well. Hooray!