Hi,
My experience w/ the 429421 is secondhand: a buddy uses that mould and sizes his bullets to .430" to use in his 629 S&W...
Dunno if he's ever slugged his barrel, but conventional wisdom as I learned it says go 0.001" over jacketed size for cast bullets if you haven't slugged yours, go the same 0.001" over barrel size if you have. Since a jacketed .44 bullet's generally gonna run .429", it seems .430" is a good starting point. If I had to bet on it, I'd think he used the same "conventional wisdom" choosing a sizer...
My buddy's Smiff likes .430's: my RH does too, and I haven't slugged it. We use different molds, but both use the Lee sizer. So I'd say unless you DO slug yours, you could do worse than get the .430" first...
Rick C