What is the deepest pocket cut can I make with a 201 end mill
Depends how deep you set the 201 endmill.
Ive found from setting that endmill specifically in securely, you have 44mm. But that is not a working height, thats exact stock to router.
The length of the flute.
Anything deeper the shank will contact the stock and cause burning in the case of wood, broken end mill in the case of aluminum.