It is my experience, not only with my 6.4, but with most engines all the way from small cars up to 50L+ diesel generators that oil temps like to sit between 200-255 depending on how hard it is being worked.
I will admit that those temps seem incredibly high, especially if you come from the old-school of small block Chevy's or other, older engines in general. My friends who race dirt track run SBC's and they start to get spooked when the coolant temps reach 215-220. The materials used in the castings of modern blocks, heads, et al are not what they used to be, in the sense that they are much purer, higher quality, and are designed with the higher temperatures that must be hit for emissions and fuel efficiency in mind.
So with that in consideration, the idea that it's too hot for your liking, may very well be the case, but that doesn't mean that its too hot for the engine's "liking". I mean really, aside from some obvious design defects, if the high temps were truly a problem for modern vehicles with all their heat blankets and plastic coverings that hold in heat, we wouldn't be seeing vehicles that routinely last for many, many more miles than we saw back in the days of conventional oil and paper gaskets, etc.
Normal changes with time...just like its now normal to have an engine that runs with a 10/10.5:1 compression ratio on pump gas, whereas back in the day 10:1 was a fairly high performance build that you needed to be running at least the higher octane fuels, and most everything in stock form was 8 or 8.5:1.