Hey Cam!
Someone from 25 will probably have to pop in to clear up the details, but here is what I know. 25 does use a 6WD with no drop. In the past, they have even gone up to 8WD, still with no drop. They use what has been termed as "Brute Force" turning; no tricks, no mechanism. It's all drive train for them. From what I recall, the secret lies in the wheels. Those massive drum wheels 25 has used in their drive system for years are from Skyway. 25 sands down the wheels so they are slick, and then cuts into them and adds tread as necessary. Here's a little more info on it:
25's Tires. While the thread is over 10 years old now, I seem to recall a thread in more recent years where the process is verified to still be alive.
Like I said, an actual member of 25 is going to need to provide the details, but that's the just of it.
EDIT: Here is a more straight-forward description of the design from a member of 25 -
Link
When it comes to drive systems with speed and power, you'd be hard-pressed these days to find a team who surpasses 25 in both respects.
Regards,
Leeland