If you've got a 1300w amp, you'd have to be riding -3db to be pushing 650w continuous. That's very very high.

What's the sensitivity of your cabs? Do the math to figure out what 1300w continuous would do compared to say, 130w continuous. It's a 10db difference, which is significant - but chances are 130w will be plenty of power for you RMS.

On that note, most of the time I try to run the amps at -20db on average. In your case, that would be 65w (18ishdb gain over stated loudspeaker sensitivity). Lets say your loudspeaker is rated at 100db 1w/1m - 118db is pretty darn loud.

It sounds like you're small potatoe's, as am I. Run the amp at -20db and you should be solid.

Side note - is there a way to calculate at what voltage the loudspeaker reaches xlim/xmax? I believe it's an exponential formula right? My gut feeling is that this cannot be calculated by T/S specs and has more to do with construction materials.