Ascend Charlie, please look at paco’s graph, which quite clearly shows RoD REDUCING with increasing speed, up until the point marked ‘endurance’.
Paco, you seem unable to read your own graph.
“And anyway, how can you go faster if you are staying below min power speed?” WTF?? You lower the nose to accelerate, just like in powered flight.
I’m guessing you two have never actually autorotated anything. a vertical autorotation has a very high RoD. This reduces as IAS is increased up until around min pwr speed (the bit marked ‘endurance’. RoD then builds again as IAS increases.
I have demonstrated this in live aircraft hundreds of times.