The sized bullet daimeter in relation to the bore daimeter is a critical component for accuracy. For 44 & 45 caliber bullets, my preference is to size 0.001" - 0.002" over the bore diameter. For bullets in the higher velocity ranges, the harder metallurgic composition is a definate asset, as are gas checks.
Back to specific bullet designs and configurations, for the 44 Mag handgun my all time favorite is a hard cast Lyman # 429421 PB, about 250grs. For the 44-40, I've found something along the lines of the Lyman # 42798 PB, 205grs works well.
In my Marlin 444 the two cast bullets I use I get from a guy locally. Both are a 'Keith' style, one is 250grs and the other 325grs, both with GC's. The 250 also works well in 44 Mag handgun and one of these days I'll try the 325 in the 44 Mag as well.
You mentioned possibly using a six cavity or gang mold. Unless you've done a fair amount of casting, I'd be tempted to leave that for consideration down the road. For the present, make a few at a time and concertrate on a quality effort rather than quantity.