I would use fans on the Quark with that setup.
My e-maxx running 14 cells, 51/13 (and stock diff gears), 7xl, Quark with the heatsink from rc-monster, one 40mm fan and a 3'' fan on top of the motor and ESC, and it couldn't finish a 5 minute race without thermaling. I was told by sky & technology that I'm over geared :031:...with a 13t pinion!
The Quark is a nice ESC to drive with in terms of smoothness, but I don't really have much faith in its capabilities at the moment.

You really need to do some kind of heatsink mods. I would just pull it apart and use thermal adhesive to bond it to the bottom of the case.

Yeah, I will probably do that once I get this one replaced, since it would thermal when the casing was barely warm you can tell heat isn't transfered from the inside to outside well enough.