If you're talking about chain hoists similar to CM Loadstars first off: no, no, no, and no again (yes I will continue to
beat this dead horse hypothetical situation or not). If you had chain hoists actually designed for performer flying (they do exist) then those lifting devices would have been built with an adequate
safety factor and provided you and the manufacturer agree as to what that should be (perhaps your insurance company says you have to have a 20:1
safety ratio or something extra high like that) then you could use those lifting devices for their full rated capacity.
What is more common when talking about using a
winch to fly a performer is to use a drum
winch similar to the
BigTow Series that is specifically rated for performer flying at the speed and capacity that you need. In this case you would also be able to use the
winch at full rated capacity (you would have spec'ed the
winch for any above-and-beyond
safety factor when ordering/renting) and if you used a multi-line
winch then all lifting points could run back to the same lifting device which improves
safety by preventing a situation where lifting points are moving at different rates of speed or some are moving and some are not.
To answer the question you asked, 3/4 ton chain hoists do exist, but they are very uncommon. In most situations it's much easier to just get 1 ton hoists.