Gas turbine propulsion

I am curious to know about naval gas turbine propulsion. I have heard from a knowledgeable source that the power output of turbines might be able to be increased considerably beyond the nominal figures. We now have some quite large naval ships, such as the new American helicopter carriers, that are gas turbine powered. We could be talking 40,000 ton or larger ships. If we want to speculate about maximum speeds, we would need to have some idea about what is possible.