** Note, I would like to clarify somethings before presenting my calculations for these various hubs.
This is a super crude possible torque index based just off the idea that you can saturate the whole flux gap area with a given amount of flux. The motors with lots more copper and mass are the only ones that can survives this absurd torque condition for more than a second or two, and that's why your x5 rips and survives it where the lighter hx35 would go pop, but just before it popped, it should be capable of these relative torque outputs.
That's why it's my own screw-ball goofy unit, made up just for the wacky mad scientist types who are looking to push these limits of exploding the motor (and likely the controller as well) for 2 seconds of intense thrust.
As a unit to relate how one motor will perform over another in the real world, or which will deliver a better riding experience, or which will win on the track, it's completely useless.
It's just a goof-ball unit to relate which could produce the biggest torque before it exploded into plasma, and it may not even be correct for that, because it's based on the assumption that they all would be using the same materials with roughly the same saturation flux density in this gap, and I am not a motor expert by any means, so it's just my best guess work.
I dont understand your math but how many "MTUs" would a cromotor have?
Clyte 40x series = 4.2cm * 17.1 *3.14 * (17.1/2) = 1,916 MTU
Clyte 530x series = 3.3cm * 20.5 *3.14 * (20.5/2) = 2,177 MTU
Clyte 540x series = 4.0cm *20.5*3.14 * (20.5/2) = 2,639 MTU
9C = 2.8cm*19.8*3.14* (19.8/2) = 1,723 MTU
Clyte HT/HS35 3.5cm 19.8*3.14 *(19.8/2) = 2,154 MTU
CroMotor 5cm*19.8*3.14 *(19.8/2) = 3,077 MTU
MagicPie 1.8cm*3.14 *26.5*(26.5/2) = 1,984 MTU
The larger diameter CroMotor 2.3cm*3.14*26.5*(26.5/2) = 2,535 MTU
The Farfle custom 2pi = 3.6cm*3.14*26.5*(26.5/2) = 3,967 MTU
JohnInCR's HubZilla = 5.0cm*3.14*27.0(27.0/2) = 5,722 MTU
My deathbike 6,574 MTU
To be perfect, this unit should have winding factor included (the average ratio of teeth from a given phase set that are lined up properly with magnets when energized), except... it's between 0.93 and 0.95 for all these motors, so I'm just neglecting it. Also, I realized that Pi is a comonality, and this is a comparison unit, so it could be dropped... but I all ready put it in, it's my unit, and it doesn't cause any harm.
So, this unit estimates that for a given stator material saturation (which is about 2T in normal stuff, some RC stuff may have exotic cobalt alloys and be a little higher, but hubs are all the same stuff), the theoretical torque it could achieve if you were sending it every bit of power it could handle until it was at the limit of saturation. So, to determine a way to relate acceleration capability (or thrust), we need to relate to tire size as well. So, I'm going to call 24" tire a 1 multiplier (because it makes things easy when thrust is also ft-lbs of torque). This means a 20" wheel would be a 1.2 multiplier, and a 26' wheel would be a 0.92 multiplier, and a 29" wheel would be a 0.82 multiplier.