What's also interesting is that all the wheels roughly weigh 1kg (TX standard is lighter and I never had access to a 28 GT leather rim). The GTE rim's weight is concentrated more on the thicker ring on the outside to make it closer to the 30" inch wheels in terms of rotational inertia.
I did some experimenting with iRacings Wheelcheck app some time ago and sadly don't have the data anymore, so I can't add a legend for this diagram, nor can I add titles or axes label, but these were the results from the step test:
In the first diagram, you see the wheels starting at 450° to spin for a set amount of seconds with maximum force in negative direction, then the maximum force is applied the other way in positive direction and some time after that once more in negative direction.
First graph is a degree vs. time graph and the second is supposed to be a radians/s (angular speed) vs time graph (the units on the y axis are wrong though).
Maybe you can see 2 sets of 4 curves each in those graphs. The set that spins faster belongs to the T500, the other belongs to the TX. The 4 curves of each set are the 4 different rims (TX-standard rim, T500-standard rim, GTE, 599xx). The yellow-y-est, fastest rim is the TX-standard, the others are really close together and almost make no difference.
The real difference then is in the longer lever you have on 30" wheels, meaning that on 28" GTE, the forces seem stronger.
I also want to add that the 599xx alcantara rim will clog up over time like a suede rim(just a little slower than suede):
just to show, what I mean with "clog up"
Best ways around this are a) use gloves when racing hard or b) clean it with a toothbrush and water ~every month(depending on how much you drive), pat it dry with a towel, let it air-dry further and then hard-rub/twist it with a towel to roughen it up again, so it regains that soft-fluffy texture (you can use the blue side of an eraser for some extreme spots).
_/¯