@FractalAudio Just a small note on the 5150 model.. I had some fun this weekend with the real amp and got a DI out signal from the head while plugged into a standard Marshall 4x12 B straight cab. Applied the cab in the FM3 afterwards.
I did a comparison with the FM3 and it looks like it is a little rougher sounding than the real deal. I can do a sound clip of this. Basically the thing that you described as rubbing two rocks vs rubbing sandpaper. The 5150 in Cygnus is amazing, but should be a little less rough sounding in the low end and more squishy. Otherwise it's insane!