Whenever I am not on the brakes at a HPDE.
The N52 is definitely strongest between 4000 and 6000 RPM. And it really is a wonderful motor - just less HP than most everybody else on the track. I often have instructors saying "More Throttle" coming out of a turn when I at WOT already.
I WOT once in a while on the public streets, but I like keeping my insurance rates down.