No.
No.
30-31mm is a very good xmax, but hardly anything new. Subs like the old XXX and W7 have been in that range (slightly higher actually) for many years now.
xmech is not 'harmful' excursion, its excursion the sub can produce before physically bottoming out (on the motor, suspension, or frame) and ignores distoriton or motor force levels (which is why you think its harmful, but it is not 'harmful' to anything but linearity)
Yes that is 54mm one-way linear.
Not even close.
You are correct, if you use the overly-small enclosure size recommendations RE advertises. But its not cabin pressure that becomes a limiting factor against motor force, its back pressure in the enclosure.
I dont believe an SSX motor has the potential for 58mm one-way (or anywhere close to it), Id have to see more info than your claim to believe that is true.
There is no such thing as peak-to-peak xmax. If you are referring to P2P, you are NOT referring to "xmax".
Mine too.