Astartes, grey knights and custodes

What's the power scaling between these 3 - I know obviously the custodes are all unique, ridiculously powerful and count as a win soon as 1 is deployed.

But what's the equivalency between the 3 like how many astartes would it take to bring down a grey knights or how many knights to bring down a custodes etc.

How much of a difference between the astartes and the knights and the knights and the custodes.