Did not know this. I knew it increased the octane slightly, but did not realise it was that much, nor did I realise that that is how much more the power curve can increase by; 20% is a lot! Will look into it. At this stage though, the car is fast enough for a daily driver and I see no real gain (other than spending nearly £500) on a setup.
The effective octane when adding WMI will depend on what you start with.