The US owners manual specs 5w-30 but 10w-30 is definately more shear stable. I towed a 1800 lbs (818KG) VW with my ranger 2 weeks ago with 2 passengers, no worries. Just a bit of extra work for the cooling system and brakes. That is more weight then a 4 cylinder manual transmission ranger is rated to handle.
As for the oils you listed, both are group III but they both have shown the ability to go beyond Fords 7500 mile oil changes in some instances. I am coming up on my 2nd of three 5k mile oil changes before I go to 7500 miles.
If you idle excessively you may want to go with the shorter 5k mile interval specificed in the owners manual. The dealership I purchased my ranger from recommends 5k mile changes regardless. I change my wifes mazda at 5k miles due to idling, limited use compared to mine and higher fuel consumption then I would prefer.
Have you read Widman's paper on a root cause engine failure? Its quite good. Mileage and hours can be seperate factors.
http://www.widman.biz/English/...recommendations.html