You most likely wont find a 700 lb tongue weight for the Regal. The reason for the limitation would be the frame. A bolt on hitch can have a tongue weight over 700 lbs on small trucks because of the frame not the bolts. Also the suspension and how far it will lower the car in back.
You will need a custom hitch installed so check the yellow pages.
I had a custom class 3 hitch installed on my Dodge Magnum 05,(welded) and rented a U-Haul Trailer to drive about 3000 miles to pick up a GN about a year ago. The Trailer was very heavy and I had to tell U-Haul I was towing a Honda because of the weight. The Trailer had mechanical brakes that deployed when you slow down.
The Trailer and GN weighed in excess of 6000 lbs vs the Magnums 4000 lbs. The Magnum really sat low when loaded and should have had overload springs to keep the rear higher and prevent the headlights from pointing above the road. The Magnum pulled the GN pretty well but would not go into the top gear much of the way unless completely level and would not utilize the fuel saving, run on 4 cylinders, because of the load.
I still averaged 16 mpg with the Hemi.
If the brakes ever failed I would have been in deep trouble and like others have said the load will keep you in boost most of the time.
