https://simonreinhold.co.uk/partridge-shooting/2020/12/13/steel-shot-the-knowledge
There is a bit more about it here from Simon Reinhold and goes into different shot sizes. I had a bit of a look and most of the High Performance seemed to be 3 inch. Seemed a bit confusing to me though with all the different naming. High veocity, High Performance, Ultra High Performance,