Axis has 3" coil as well, but it's NOT the LMS coil and has a much bigger motor to help absorb heat. (the only TC subs with 4" coil are the 4HP motor ones AFIK)
Below 35hz you'll notice a lot more output out of the LMS. Again you're sacrificing some >50hz and power handling...and of course the axis is a lot more money. I'm confident Axis will get pretty low too. Have you ever played test tones and really felt 20hz? It's very very low. I notice the difference with:
pipe organ music
movie sound effects
a few bass mechanik type songs with 10 and 20hz notes.