It's essentially the same cooler but the Dark Knight has a nickel plating that gives a beautiful metallic sheen. Truthfully, you might lose 1 degree, maybe, because of the nickel plating, otherwise just get what you think has the best aesthetic looks for your case. Personally, I have the Dark Knight and it is absolutely beautiful in my HAF. Very quiet, too--Xigmatek makes some nice quiet fans for these coolers.
Well, my wife--I built her new system last Friday after... well, after her aging Dell power supply died and took a lot of components with it. On my personal system I'm using a ThermalTake SpinQ--it's very pretty, it does an adequate job for a 3.2 GHz OC, but I wouldn't go any higher with it. The Dark Knight, however... her load temps are easily 22 degrees below mine, and that leaves a lot of desirable room to play.
Sadly, she won't let me play with hers ATM. So, a Dark Knight is definitely on my order list for the next build, which, according to both her and a few NewEgg reps, is at least another 8-10 months away.
Yeah, but when you put it that way I want to secretly remove it from her system and use it for myself...
On the plus side I have Wednesday off this week (my workplace has an odd rotation) and I'll be playing with her system for a few hours. It's sad, in a way, she has no idea how fun it is to sit there and really play with it.