rf power spec

This question, while simple in nature has a very complex answer.  There are multiple variables in play such as PA design, ambient temperature and the quality of air flow around the radio.

From the design standpoint, the PA in the FLEX-6000 is designed and rated for nominal 100W ICAS (Intermittent Commercial and Amateur Service) output.  ICAS implies that the transmitter is not designed to be turned on, operated at max power and left on indefinitely (that is CSS - continuous commercial service).  Under the ICAS classification for solid-state amplifiers, it implies de-rating to keep the device junction and case temperatures within their maximum ratings. Thus, ICAS suggests a limited operating or 'on' period followed by an 'off' or standby period of at least the same or longer duration.

The PA transistors in the FLEX-6000 are stout and well de-rated so that you should not expect any issue operating full duty cycle modes.  And there is also thermal protection built in that will shut down the radio before any damage can be done, which is really the most critical aspect of this question.