I have also towed with a 1/2 ton Suburban, and although the rear end does sag a bit when loading a car on a u-haul transport. But, putting the car on backwards on the transport can be REAL dangerous, as in, an uncontrollable trailer sway. I have seen a 1/2 ton chevy pickup going down the highway, with an off road tubular frame rear engine buggy loaded on the trailer backwards.
With a very slight crosswind, he was ALL OVER his freeway lane. He had real bad case of uncontrollable trailer sway. Please put the car on front end first on to any auto transport trailer. I also prefer the auto transport over the dolly. Not only does the transport tow easier, it has brakes, as mentioned before. It also has the appropriate trailer lights. Unless you want to run your own wiring to the back of your volvo ( I did when I towed my ’90 Honda Accord on a dolly), the back of your volvo will not lite up when connected to a tow dolly. No tail lights and NO BRAKE lights. Yes, the tow dolly has those lights, but they are up by the front wheels of the towed vehicle. Not safe in the day time, and Dangerous at night!
The U-haul transporters are amazingly heavy up front. We towed a V70r using one, towing with a F-150. The rear end of the F-150 was completely bottomed out.
I tow for a living and the 850 is a light car for towing I’ve towed them a lot, and long distance’s biggest concern is you know the length and have it properly on the dolly. This is what will minimize any problems, being set in dolly correctly.