Yes, I agree that copper is a better conductor than alum., but are you going to mount that Quark to a heatsink? Even then, the heat has to pass through two thermal interfaces, not just one (when in a Quark case), that will be limiting it. If I made my clamp from copper, I would maybe lower the temps by a few degrees. I just wished that I had found a smaller/ligher heatsink for my Quark, as mine is too tall for mounting if lot's of places.
This makes me want to get Mike to make my 'custom quark case' that I designed 6 months ago.