We definitely do a keydown test on all of our radios before we begin shipping. I don't have the detailed data in front of me for the FLEX-6300, but I can assure you the answer is 100W. Typical behavior on these tests in our lab is the radio will asymptotically approach an equilibrium where the heatsink's ability to cool equals the heat dissipation of the transistors. This point is well under 90° C in our lab environment and I know we have done multi-hour tests to prove this on all of the FLEX-6000 series (in at least one case, we ran them overnight).
Obviously the ambient temperature and airflow factor into this equation, so we will do shorter tests where we constrict airflow. Rest assured that the transistors (and surrounding design) in these radios are very rugged.