[Ray H]

I used to tow a 2000lbs boat with me XJ and it did wonderfully. As mentioned, the XJ, set up properly is rated to tow up to 5000. BUT I think thats really pushing it. I would not tow anything over 3500 on a regular basis and thats with trailer brakes and properly setup. I would tow 4500-5000 if it was very limited, like once or twice per year and for only a short distance, basically a situation that buying a dedicated tow vehicle isnt feasable. The situation you describe "regular towing of 4500-5000lbs" you should really get something more suited to the task.
Can it be done safely, sure it can but it would mean changes that you would have to make, like reducing speed alot, increasing following distance alot, slowing down early for turns and stops. You may say, sure I can do that stuff, but we all know it wont last. You will be in a hurry to get to the lake or tired on your way home or trying to beat traffic or a thousand other reasons and before you know it, you get complacent and its no longer a safe act.
This is not meant to be condescending, we all do it, its just the nature of things. Its how accidents happen. this is the reason why I think its ok to do on an occational basis. The complacency factor isnt there.