A closed press frame (O-frame) will be stiffer than an open one (C-frame).
The ram stroke is slightly longer for the Classic Cast (4" vs 3.5"). Also its cast-iron, versus a machine aluminum casting. The breech-lock "press features a the breech lock quick change die system that holds dies in inserts that allow the reloader to quickly remove them from the press."
I have a Challenger, and it's good enough for my loads. 0.5 MOA. Realistically, the Classic Cast might be a hair better, mostly in regards to the length of throw if you're loading long rounds. But strength wise, as beefy as these presses are, and types of loads the parts are seeing, they're even.
So for me, there's no difference. At least not enough for one to be twice as good as the other.