Yeah, I would think if you want your amp to be captured like most realistically, I would use an actual mic and not IR's. Plus it comes off as a lot more professional if actually take the time to mic a cab up.
It's honestly not that hard. Mic all 4 speakers in a 4x12, find whichever sounds best, and go from there. Put the SM57 in the sweet spot, which tends to be close to the same in most Celestions since most of them have the same diamater voice coil and many of them have teh same dustcap size (dustcap meets the cone, about an inch away). Tweak the position if you feel like it. But honestly, if the recording is not sounding at least usable in that position with the usual suspect speakers (V30's or Greenbacks), then you need to go back and re-approach the way you set the amp.