When we see the freq response of an ir, we are only seeing just 1 moment in time. Wait a split second and all those hills and valleys will be in a slightly different location. So it seems to me that you could just get an averaged freq response, one without any added artifacts, you would be fine. In other words, if you take 5 irs from a cabinate, wouldnt they all be slightly different? It certainly seems that if you strictly want the cab response you wouldnt want room reflections or any distortion from the pure cab. Any speaker system is going to excite a room at the right volume level, why would you want room excitation on top of room excitation. That would take you farther away from an "amp in the room" sound. MHO.