I have in the past towed 100% car weight, this was due to finnances not being available to upgrade the tow car . All was well most of the time until the van waged its tail then it could become frightening. The final straw was a calm day on the M25 near heathrow, traffic moving nicely (unusual) and trundling along in the inside lane at 50mph just gone under a bridge then suddenly the van wag its tail (no passing coaches or vans etc), what followed was a white knuckle ride that seemed to last for an eternity (in reality several seconds) the van took control of the car andit was a matter of holding onto the steering wheel with all my strength to keep the car in a straight line, whilst all the time the van was trying to pull the rear of the car lest and right. The van seemed to have increased to 12ft in width as all I could seen in both door mirrors was this white pendulum and there was this terrifying thudding noise. Fortunatley we managed to stop in one peace with the car and caravan intact (trousers were another issue). The van was not used again until a heavier car was purchased and even then it took a while to regain confidence. What caused the snake, only thing I could find was tyre pressure on the nearside of the van was 5lbs lower than the offside, that possibly added to ruts in the inside and the possibility of a side wind as I went under the bridge.
We know tow 1700kg with a 4x4 which is around a 70% match, no stability problems, yea there are times when conditions will make the van wag its tail but the tow car is heavy enough to immediatley bring it back into line.
I am not saying that you cant get a snake with a well matched outfit.
With over 20 years of towing experience, all year round in most conditions, would I go back to a 100% outfit ? No way. As for the 4x4 its my (legal) choice.