honestly, if you are running black pipe,
its usually best to do the max go 3/4 all the way
......because if you or the next owner might want to add a gas
water heater or other outlets someday it would
not be a big problem...
I myself would run it out of 1 inch black pipe
and reduce it down to half inch once you have gotten
into the mechanical room. putting a tee and a cap
in the line for future needs if any would arise.
it might sound like overkill,
but it dont really cost that much more
at least do the 3/4