It's perhaps worth noting that in their Standard Torch System instruction leaflet Bullfinch stipulate surprisingly large minimum cylinder requirements for the medium-sized burners upwards.
I'm not sure how necessary it is to slavishly follow their advice on this count; I have used large KW-rated Sievert burners at 4 Bar off a 13kg propane tank, when, according to Bullfinch, burners of theirs this large should only be run from a 47KG cylinder.
Of course if Bo'sun is only after the kind of Bullfinch torch that screws directly on to disposable Bernzomatic-style cylinders, Bullfinch's caveat won't apply.