play around with the citi tool here to calc voltages and check driver options
http://ce.citizen.co.jp/lighting_led/en/products2/notice_Simulator_ver5.html
also consider the 1818s which use the same holders etc as the 1212 but run at higher ~50V voltage.
benefit of the 50V is that the hlg185-48A cosntant voltage drivers up on the site are some of the cheapest meanwell per watt you'll find and the 50V citis fill them out really nice (in practice that driver turns up to 53.5V)
so as an example. lets look at hlg-320@ 1400ma with 6 x 1212s
7871 lm x 6 = 47226 lm, 308W, 153 lm watt
6 x $13.50 + $105 = $186
now lets look at 6 x 1818 on 2x hlg185-48a drivers (4.2A ea per driver, same 1400 ma per cob :
11589lm x 6 = 69534 lm, 445W, 156 lm/W
6 x $26 + 2x $40 = $236
thats 50% more light for $50 more dollars, and is more efficient.
(or alternatively 3 1818 x 1 driver @ $118, 34767 lm @ 156 lm/W)
if the 6-cob 2 x hlg185 rig was dimmed to the same lumens as the first hlg320 rig youre at an impssive 165 lm/W which may also be worth the extra $50 to you