That probably just means it's disk I/O-limited and not CPU-limited.
I just tried with an i5 quad and CPU load varied between 30% and 80%, with brief peaks at 100% - spread evenly over the four physical cores (no hyperthreading). That's also D800 files.
On the i7 3820 at work I don't think I have ever seen CPU load hit 100% under any circumstances. But I'm not looking all the time of course.