Rich,
My lead melting pot (a milk pot) holds over 4lb of lead without being too full and my lead making sessions last well over 2 hours - we roughly smealt about 40/50lb of lead on a big session doing 1-2lb dowtide leads.
The stove does get hot, but the base doesnt and when it runs low after an hour or so, we simply leave it 10 mins, have a brew, re-fill her and off we go again.
I would suggest that a Coleman is all anyone needs, unless you are going to make them commercially - the other factor is that regardless of how fast / efficiant the stove is, I still cant pour the lead, release the moulds, re load wires and stack before the lead is melted!!