IIRC, some of the BXi and TXi amps bench as low as 25% below rated to just under rated at a single frequency.... usually 50, 80, or 100 Hz.
The XX and XXV are usually spot on with regards to rated power. They may be plus or minus a few watts from rated, but the difference in output will translate to less than 1 dB in SPL.
Regardless, if your amp is 1 ohm capable, it shouldn't hurt it to run it at a 1 ohm nominal load //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif