Ford's recommended fuel for my twin-turbocharged V6 is 87 octane. They do, however, note that increased performance can be had with higher octane fuel.
There are a lot of guys on the forums that insist towing with higher octane fuel yields more power and better results. I've never had any problems with towing on regular unleaded, and the cost delta with buying premium fuel at 8-10 mpg towing, would be considerable...