I am runing the same heatsink from rapidled with two CXA3070 at 1.4A
i used the dril\taped holes for fastening the ideal cob holders, another benefit. no need to drill myself.
i use 2 120mm fans for active cooling, which is defenietly over kill.
http://www.digikey.com/product-detail/en/EEC0251B2-000U-A99/259-1480-ND/2021108
without the fans runing the heatsink is warm to the tuch. i don't have anything to measure temps or light.
i used it to supplement HPS lights, and was happy with the results.
my grow is in a 4' x 8' secret jardin tent, (2x600w) and i think to replace each 600w with 16 CXA3070, one for each squre feet, runing at 1050 ma
maybe i will use less watt finaly, but it's still has to be 16 COBs on 4 bars
i plan to use 4 heatsinks\bars, 38" each of them.
i want to minimize mess, and to be able to look at the garden with clear view. so 16 indipendent hanged passive heatsinks is not an option
the 4 light bars will be of course the heatsinks themselves.
one option is the 3.945 HS, it has a nice base of 0.375' and long fins.
can be cooled with two 92 mm fans, should be more then enough.
can use thouse - less then a watt each
http://www.digikey.com/product-detail/en/HA92251V4-000U-999/259-1614-ND/1937331
other options are the 3.500" or the 4.230. both with thick base and short finns, probably will have to use stronger fans.
i want to connect every two bars together, so i can hang them as one peace. i don't want forest of rope ratchets from the ceiling to the lights
my grow from today -