If talking about land based sites, most, if not all, of these have a heat recovery system within the exhaust gas stream to heat water and power a steam turbine.
Combined cycle - Wikipedia, the free encyclopedia
this being the case the heat recovery will lower the final output exhaust plume to a fairly low figure.
Not strictly true. Granted, most of the GT power plants built nowadays are "Combined Cycle" (where the exhaust heats water to power a steam Turbine), however there are still a fair few "Open Cycle" plants around. I work at one such plant, and the GT exhaust exits the top of the chimney at around 500 degrees celsius...