OK OK, you can travel at such a speed if you're a nit and don't slow down if you need to pass close to someone, but if the path is wide enough, a fast cyclist can pass someone at full gas without being a hazard. For example, if someone's cycling near one edge of the 10m-wide tarmac section of NCR1, their speed shouldn't bother a solitary person walking along the other side, should it?
I realise this is all a bit hair-splitty but I get a bit sick of the "cycle tracks are only for slow pootling" brigade. If we build them properly, including being big enough for the volume of traffic, they need not be, although of course congestion is possible, the same as any road.