I had a friend who had a friend who said that he read on an "official" website... yak, yak, yak.
The 2009 6.4 twin turbo I owned and drove/hauled with for more than 65k miles did a great job with NO issues. What you have to be careful of (really with any late model diesel) is that the 6.4 will make more horepower for the least amount of $$$ invested becuase its fuel system and turbos were capable from the factory. Therefore, many people pulled the DPF (maybe bypass EGR too) and put tuners on them and ran the heck out of them. I actually prefer the 6.4 over my current 6.7 but the new 6R140 six-speed automatic transmission with SelectShift is awesome.