I use the 450 for about 3 years now and never had a thermal-shutdown.
In fact the 450s are NOT realy designed to lay them down on a stage. Just have a look at the back and follow the ribs of the heat-sink.... to achieve airflow they need to be positioned vertically.... upright position.

I do not agree with mikeathome, telling the EONS blow away the Mackies. EONs sound 'poor' or flat compared to 450's.

btw. I would never 'spoil' the soundquality of 450's by using them only for monitors on stage. (kidding, but true !)