I always run the cheapest gas I can in my crossfire. haven't a single problem yet. Though there is a slight noticeable loss in power when dropping from premium to low grade. I just let the computer handle the timing adjustment.

I haven't had time to research how the XF heads flow coolant, but most cars these days are reverse flow, thus cooling the heads before the block, and allowing you to run higher compression engines on cheap gas.
I know the 1990 - '95 LT1 Impallas and old Police cars had 10:1 compression ratio. And they used nothing but the cheapest gas possible in those squad cars.