mulepacker,
I think it all boils down to comfort level. With your vehicles, I'd say any SL rated oil should go 3k miles easy. If you want to extend to 5k miles, then step up to Jelly's suggestion of a diesel-style dino oil. 10k mile changes? Any premium full syn (Mobil, Amsoil) or Group III diesel oil (Shell) & maybe one or two semi-syns (Schaeffer's or Saab's OE?) would take you that far without a problem.
Do a search on this BB for "aunt" & you'll find several threads which refer to a Mobil 1 short-trip/extended-drain test (it's been called both "Aunt Minnie" & "Aunt Millie"). Basically, the oil was claimed to survive under more severe conditions than what you've got.
Your driving habits sound about like ours, & I'm comfortable running Mobil 1 (or Mobil's Delvac 1, if cost & availability were closer to M1) for 10k miles/1yr in my turbo engine. My UOA at almost half-way shows the 0W-40 pretty beat up, but not enough to worry that my engine's not being protected for the remainder of the year.
I like Patman's theory of using a thinner oil for a car that sees all cold engine, short trip service, but I'm not willing to try it in my turbo. (Maybe he'll give it try this winter & let us know how it fares?)
With my non-turbo car, I've only put about 4k miles on it in the past year. I started out with M1 15W-50, but my two top-ups (about 4oz each) have been with M1 10W-30 & Saab semi syn 5W-30. Once I reach 5k miles (another 3+ mos?) I'll change the filter & run a UOA, then take this same batch out to 10k miles.