Damn......guess I have been messing up for these past 6 years or so and 100s of gigs.....dang it - I had no idea!
But seriously though, folks...
I play my 4Pro through the 610HLF and have never experienced an issue....I play with the EQ ON but flat, the bass at 2:00 the Midrange at 3:00 ad the treble at 1:00.
I have the gain at 3:00 and adjust the master as needed for the room....I do NOT use the compressor.
It is a BEAST.
That having been said, if you're trying to break windows, you will probably blow out the cab well before that happens. You DO NOT need an additional 15. Period. End of story.
Push ANY cabinet too hard and bad things WILL happen.....
Cheers!!