To be honest they'll perform about the same. The Z11 may win in stock cooling out of the gate, but they are designed very similarly in terms of airflow. If you plan on doing dual GPU setups, the Z12 may be better, as you can intake cool air from the bottom directly at the GPUs.
Z12 it is then! Thank you so much!!
No problem, enjoy it Since you've decided, I'll let you know I personally prefer the Z12 over the Z11 in looks too :P but I promise, my recommendation was purely un-biased lol