Well a forge only warthog could be different than the average warthog with a turret. They could change the setup of the normal hogs and have it so the engines in the back replacing the turret and since there's more room back there then up front it could be pretty fast compared to the others at least by 10 or 15%. And the front could be a place to hold weaponry. However the hog could only hold two people but that's not much different from gameplay anyway.
Although that warthog could have (i say could have) a booster canister with a limit that doesn't refill located beneath the hog and, when shot or hit by a grenade, could go boom and completely destroy the hog.