I normally run Rotella T6 though have cheaped out with T5 now and again for topping off between oil changes. Have read tests that Mobil1 is better (though only slightly) so far as high pressure scratch/wear resistance. Probably biggest thing in our engines that may affect is rockers, since we have roller cams. Plenty of guys running dino Rotella or Delo though. Don't think our engines have many oil related early failures. MNy personal reasons for synthetic are mainly around higher temperature tolerance and concerns about turbo life and the turbo heating the oil, not so much the engine itself. Cold starts sure are nicer with the 5w synthetic too, oil pressure comes up quicker and it'll crank faster. In my farily uneducated opinion though, T5 is a fine oil for our engines.