Per the Wetsounds specs thermal RMS ratings are:
Those are good guidelines since Wetsounds knows their product.
In being conservative, I'd stick with anywhere from 75 % of those numbers up to the full rating. You can bet that many have run 25 % more power with no problems. It depends on how the amplifier is rated (12.6V or 14.4V), how you execute the installation, set-up and tune the system, and your understanding of audio related to how you either use or abuse your system.
Personally I like to exceed the rated power. I can never have enough dynamic headroom for the type of music I play. And I would never have a failure because I have zero tolerance for distortion and know how to set things up.