okay so I ran a test with a fellow staff member, with ROR's diff capability
-open diff
-locked diff
-split diff (technically the diffs are open but the diff will give equal power regardless of wheelspeed, so in essence a all wheel drive system)
right off the bat I can attest that adding a axle line to the truck file affects the truck immensely, wheelspeed and traction was up near tenfold (x10) from a box stock V4 truck, basically you could go from a dead stop to max top speed in under 2 seconds.
An open front diff made the truck handle like old american rear wheel drive car with the front diff having no part in helping the truck pull at all, once you cornered hard, which you had to do to make it even take a set to turn, if the inside front tire came off the ground, power went 100% to the rear and resulted in some rather interesting situations and 9/10 resulted in a roll over.
A locked front diff the truck was a freaking land missile, you had to quarter throttle around the turns or the truck would throw itself around immediately. basically you hit the throttle and it was going to go in the direction you were pointing with no finesse at all.
Split diff in the front was interesting, it seemed to be a middle ground but like I stated above just adding a axle definition line to the truck file and a trucks throttle response and traction went up regardless of diff selection.
We did a average run time on Arlington 2012, this was based on a 10 runs with the best 5 picked
Locked ran a average of 18.324 and had the fastest time of any setup at a 17.83
Split diff averaged 18.648 (fastest time this setup got was a 18.20)
Open diff averaged 19.448 (fastest time was 18.87)
If this was the direction we would want to go this would require a good overhaul of the trucks traction and power setting to try and make it work, while this will be noted for future updates, this idea probably will not make its way into the update currently being worked on