The modular engines are pretty bulletproof. We've got some fleet vehicles at work thats got 300,000+ miles on them with nothing but regular maint. I agree with arggh, in your area 10w-30 or 10w-40 should do nicely. If you notice a bit of exhaust smoke after idling (valve seals) for a while you might want to step up to thicker oil, its a common issue with old 4.6L's. I used Rotella T 15W-40 diesel oil in an old crown victoria after it starting burning oil through the valve seals at 90,000 miles, it went on to a ripe old age of 200,000 before being traded.
honestly, with that kind of mileage I would use any available brand of oil, just stick with the factory oil change intervals and regular maintenance. I'd be willing to bet the tranny will die LONG before the engine goes.
