As a matter of fact, last Dec. 29th. I spent one of the longest days of my life trying to traverse the fair states of New Mexico, and Arizona thanks to Rt. 40 being shut down due to a snow storm. To be honest with ya, I really wasn't paying much attention to the gas pumps octane ratings, and I wasn't driving my Crossfire either. But the Crossfire I was following fueled up at every station I did, and had no gasoline related problems, so if it was low octane he didn't notice any difference.
I'm not saying you can't run cheap fuel in your XF, I'm saying you shouldn't. I just think that you are doing everybody who plans on keeping their car for an extended period of time a disservice telling them it's OK to run low octane fuel.
Probably more than anything else, I was taking umbrage to your statement that the Crossfire wasn't a performance vehicle, when I think most non-SRT owners on this forum would disagree with that statement as well. But knowing what your expectations are, then I see where you're coming from.