Buffalo Arms has some wonderful moulds in .50.
You were likely aware of that. My brother bought
one of their 600gr. moulds and with 91gr. Swiss 1 1/2F
gets almost 1,300fps and rings the 1000 meter buffalo
like a bell.
With smokeless and a .030" card under the bullet, it should
make about 2,000fps with that 600gr. bullet, if you want.