I routinely run 550w into hl10's which are 300w speakers. And I run them right at that limit. They never break a sweat. When I'm running just one pair, it's 1100w from the bridged amp. I don't push it to the limit when it's just one pair, but I also don't worry about it.
I've even got them in Beta 10's. Pretty small sinks in the cab I'm using, but I'll take any protection I can get. I see them more as insurance rather than for increased power handling. If it it keeps you from losing a driver at a gig, they're worth every penny.
I've still got to get around to some more heat testing. I got an RF thermometer to put in the vc and be able to read it remotely, but it's my busy season. Probably won't happen until the fall.