I will speak from my experience.
If you are running continuous music playback and you are running heavy bass music which is pretty much standard with today's hip hop and dance DO NOT and I mean DO NOT power them at the program rating which would be around 3000rms if I am not mistaken for the JBL.
Power them around 1600 (JBL) and you will be golden. I have setup a few different dual 18's in a few different venues and they blew, not becasue the DJ is an idiot, becasue the woofers were over driven. I switched out the amp to match the continuous rating of the subs and everything was better. I could not tell the difference in sound either. (SPL)
If this is for live situations,then that is a completely different story.