Since you went with the Nitecore for reliability (heck I have two!) remember, the Quark has a 10 year warranty on it from the same people who first offered lifetime warranties on Fenix flashlights. I hope you got your D10 from 4sevens, because they warranty their Nitecores for life as well (just started that policy). I think you'd have to work VERY hard to find somone on this thread who'd bad mouth 4sevens' customer service. They're second to non.
On that note, I just got my Quark AA. To my eyes, it's hotspot and spill are brighter than both my D10's. Please keep in mind I'm comparing it to GDP and Q5 d10's . . . I never got the R2. Also, you didn't mention tint, and I hate it when people start to talk about trends in tints as belonging to this model or that manufacturer. Most assembly lines do NOT I repeat, NOT verify tint before the LED goes into the build. Most vendors who offer warm or neutral tints do so after they come off the assembly line. Case in point:
I've seen people talking about the great neutral tints of both GDP and Q5 D10's. I've had two D10's, one was slightly green. I sent it back because it whined too much. The next one I got didn't whine, but it's the greenest little light I've got, foget that, it's the greenest light I have. My GDP is the second most blue (more purple really) light I have. I actually EDC it because the beam profile is so smooth with the best transition from spot to spill that I've ever seen. After owning the EZAA, though, it's hard not to notice that violet hue.
Fenix LD10? I've got one that arrived last week from 4sevens. Not bad mouthing either 4sevens OR Fenix, but that's the MOST blue light I've ever seen, and I'm comparing it to those cheap dollar store blue lights. Still, though, I like the design of the LD series. I have an LD20 and I ordered the LD10 as a gift.
jhc37013, for your purposes, the LD10 and the Quark AA have the same UI, except the Fenix LD10's low is still high enough to wreck your night vision. The Quark AA: Turbo is higher and when you loosen the head, you've got a low that's 0.3 lumens. Perfect for night vision. There are two more modes in the Quark AA than in the LD10: beacon and moonlight, which is the low low I was talking about. If that entices you (don't forget about the easily removable clip) try this new light.