Spartan has a 6.7...
Haven't heard anything beyond that.
H&S makes one too
I know (as well as everyone else) that the 6.0 will have problems if you try to push them. But from everything I have seen with the 6.4 they seem to be solid with nothing done to them till at least 650 700 hp,, at that point it is tough on any engine IMHO. Dont get me wrong I am a dodge lover, but I have to credit where it is due. The 6.4 is the real deal, there isnt another engine going as of now that with just a tuner and DPF delete you can be pushing 600 hp and get over 20 mpg