I do not understand why you increase the number of GPU on your rig? It doesn't make any sense. It seems to me that 6 GPU is the optimal amount. From the fact that you increase the number of GPU to 12 PCs you will not win anything. This rig will take the volume is the same as a 2x6. In case of breakage you will have 12 GPU. The possibility of a fire is also higher. And most importantly, the price of rig 12 GPU will cost the same or even more than 2x6.