It becomes annoying above 70ish MPH. I tend to drive on twisties at slower than that, and with earplugs. The earplugs drown most of it out while letting in the motor noise.
The noise from my BB almost disappears above 60mph. Its quiet for first 10 miles from cold. With my new chassis & NVH kit its changed a bit & now most noticeable around 40 - 45mph.
