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!
Can't tell much if anything about power compression with this data. The tests being at 2 frequencies nearly 1/3rd octave apart can easily account for 2.5dB itself. Not to mention one has a much lower impedance than the other. Not really apples / apples at all.
Luke even as strong as those drivers are Id be careful with doing this type of stuff. You may cook one. Use as many drivers as possible so they don't get heated as much.