From testing a variety of heatsinks, I found the Alpine 11 slightly outperfpormed the Freezer 7 Pro. The Freezer 7 has a lot more surface area and heat dissipation capacity, but it uses the heatpipe design with a relatively small copper pad. The Alpine 11 is one chunk of aluminum with a thick base and relatively thick fins, so it moves heat faster than the copper pad heatpipe design. So for our purposes if you wanted to passive cool that 66W COB, the heatpipe design is unnecessarily expensive and less than optimal. You could use 10" X 10" HeatsinK USA ($35) or one of those big round passive heatsinks. It would run even cooler and put out more light mounted on a $10 Alpine 11 with fan running at 6V.
1 pound chunks, Alpine 11 and Rosewill RCX-Z1
But all that is splitting hairs anyway and wont make much difference in light output. To
really make a better light we have to look at current droop. With a 4K Vero 29 @ 1.75A it would be 130lm/W. With 4K CXA3070 it would be 135lm/W. With a pair of CXAs at .9A it would be 162lm/W. (I know most of you guys already know this.)