If you arent braking 150dB with two 15's of that magnatude and 2400w you are doing something wrong. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
and if two of thoes 15's can do a ~148 with only 600w, I dont see why they couldnt do a 153 by giving them4 times the power.
I'm sure you know increasing power can do a lot of funky things though. It can make inductance drop slightly because you are increasing current. It could also make the box start to flex, however that would make the impeadince go down even more. I'm assumeing it is built solid though so that varible should be taken out of the equasion. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif