How fast? More specifically, to make good progress but be generally acceptable to the forces of lawanorder? I don't usually start filtering until the traffic, and therefore my speed, has dropped below about 30mph. I then have a sort of hysteresis where I don't stop filtering until I'm doing above about 40-45mph max. I don't filter at more than about 5-10mph above traffic speed. ISTR being told on last year's advanced riding assesment (by ex class-one police rider) that filtering up to about 45-50mph was OK, which surprised me. Did I hear right?