The takeaway from all this is that if you truly want the sound of amp in the room the best way to get that is to use an actual guitar cab. This isn't to say that far-field IRs are useless. They will give you a roughly similar sound to a guitar cab but it's just not the same.
Thanks for the great explanation. Maybe this is why I haven't found an FRFR cab I truly love. I always lean toward a guitar cab for the live application, and go direct to FOH. Of course, as we all know, our ears are different. What sounds good to one may sound bad to another, which is why I'm always asking opinions about the live sound of the rig.