“Siemens unveiled its new HL-class, the next generation of larger air-cooled gas turbines that represents a push for higher power plant efficiency “ a must for operators nowadays “ with the gas turbines realizing more than 63% efficiency in combined-cycle operation, and moving towards the 65% mark.”
https://dieselgasturbine.com/new-class-gas-turbines/#.XMdYnuRYbNM
Your “high 30’s” probably does represent the typical reality of the installed base, however.
gas turbines cannot supply the power a coal fired or nuclear power plant. how mant gas turbines can run for 2 years supplying a 1000mw without stop? how many can even supply 1000mw? Gas turbines are a small temporary power supply.
Gas turbines can be much more efficient than conventional steam power plants. I see they can make 400mw and adding a 200mw steam cycle to the exhaust would be a total of 600 mw.
But gas just aint that cheap right now.