I have both of those Lee moulds.
The 456 is too large in diameter to seat in any of my Piettas or Ubertis- get the 450.
I've had better results from the Lee conicals for accuracy and better downrange energy than any of the other, more traditionally styled conicals.
Barney Fife: "Nip it, nip it, nip it!"
Andy Griffith:"Oh now Barn'...."