Here is my take on it... IMO....
Ski Doo, Arctic Cat, Yamaha and now Polaris, on the Factory installed drivers on the Race sleds all run COMBO drivers (different than a true extrovert driver)
There is a difference between an "EXTROVERT" driver and a "COMBO" driver
A combo driver [eg Avid] drives from both the involute "nubs" on the inside of the track and the windows of the the track .... it does not rely on the "teeth" of the extro-portion of this "combo" unless you start to ratchet. A TRUE extrovert does not drive at all from the involute nubs on the inside of the track (eg the center driver on a dragon).
Some stuff I've learned from the diff engineers in the sled world.
Looser tracks allow the paddles to fold over easier... a part of the equation that most dont think of and is the MAIN reason why (I think) Jack Struthers says that a tight track works better than a loose one...it hooks up better, expecially in more setup conditions like on a track or hill-drags, or spring time climbing (or our average Sierra cement). He has done extensive testing with track tension.
The people with Extrovert (AKA combo) drivers seem to want to run the track real loose and feel it frees up HP...a loose track allows for distortion of the track (the track "wrinkles" and allows the paddle to lay over a bit) as it leaves the driver and makes the track more suceptable to "stabbing"... With the extros, I dont look at them as a way to allow a track to be run looser... I look at it as a prevention of ratcheting in the high-demand situations.
I think the "combo" drivers are the best option, but run almost as tight as the stock drivers AND run the more slippery hyperfax as well as popping back on some idlers for spring conditions as well.
Combo drivers, IMO, are mandatory on high hp sleds... BUT they should be run at the correct, not loose, tension... similar to normal tracks/stock-drivers.
When they are running normally, not ratcheting, the teeth of the combo are not even contacting the track or the clips and only drive from the involute portion on the inside of the track.
The first of the M-series cats had poor geometry that tightended up the track when it worked thru the travel and caused all kinds of problems that was the big factory push to factory "combo" drivers and the one that gave the extros and stabbing a bad rap.
The Polaris Race sleds are taking much more punishment on the circuit than almost any cliff-dropping Mountain rider will put on thiers... all with Twin Combo Drivers, shortened rail tips and PROPER TENSION...
When a dragon does start to ratchet, with the center extro... you dont have much "tooth engagement" into the track to transfer power to the track (only 4 or 5 teeth on a non-clipped window) and, this puts a lot of load on the center of the fiberglass rods in the middle of the track... I've seen 2 dragon tracks from last year running turbos that have multiple broken fiberglass rods that go thru the rubber on the track, visually aparent. If you ratchect a dragon... you are putting a lot of stress on the track and reinforcing rods. Only the 163" models got the center driver last year, I'm curious to see the results this year as they have more wide spread use.