i wasn't suggesting that you hadn't done it or didn't know. i was just laying out my logic. on second thought, in this test, doubling the current and doubling the power are looking at the same thing. [they probably always are, but with amps and speakers frequently folks refer to the "watts" as the volts/dc r not the actual, and varying, impedance.]
as for testing the same freq., that might make some sense as the contribution from the room (and possibly the sensitivity of the horn?) may be a little different at the two different frequencies.
with that much power compression, i'd be worrying about cooking the drivers. don't want to see that!