Alright, I've modeled all but the IA Lethal Injection, I can't find any T/S specs for it.
All graphs are held constant with 600wRMS input power.
Alright, color codes -
White = SSA Icon 15
Purple = Mach5 IXL15.2.2
Red = Fi Q 15
Blue = RE SE 15
Green = IDQ15v2-D2
So it would appear that the IDQ, FiQ, and SE model out very similarly as far as SPL and roll off go. The Icon and IXL have a similar roll off, but you can see that on the same power, the IXL lacks in output significantly.
I'm between the FiQ and SE myself right now.