When I hear questions like this I think back to my 1991 F250 with the most powerful engine sold by anyone that year for trailer towing, 230hp. The current 4.3l is 285hp. I often went over 10,000lbs with 230hp and go everywhere I needed to go, and that was with a 4 speed transmission.
I could go farther back to a 1978 Chrysler that with towing package was rated for around 7,000lbs with 150hp. Again, the most powerful engine available for trailer towing that year. That was a huge step up from the 1966 Rambler with a 232 cubic inch 6 cylinder that we used for a while to pull trailers.
I feel sure that you could get there with 285hp. The engine will rev a little higher but it is not nearly as noticeable in the new engines. It just depends on how big of hurry you are in and how often you do it.