The Compressed Gas Association revised (2006) the maximum recommended withdrawal rates for acetylene down from 1/7 cylinder capy per hour to 1/10 for intermittent use and 1/15 for continuous use. This short article provides some interesting details on the potential failure modes and effects:

Fuel your safety knowledge - TheFabricator.com

I now realize that I've been exceeding the old recommendations, never mind the revised ones. Since I have recently come to appreciate a rosebud and large tips for the large items it looks like I'd need an AC5 cylinder; too large for me to transport and handle. Based on Smith's data an AW205 looks like the largest tip that would comply. For that reason I switched to LP for lugs, crowns, BB shells. My AC3, 75 cf Acetylene cylinder is only for the smaller tips and frame items now.