I wonder if they're even worth the effort, since no one can actually tune the XF ECU to really take advantage of the air flow.
You might be better off buying your own ecu and starting there, learn how to use the software and play with the computer. Next you should get your self a data logger, so you can monitor all the engines sensor outputs. This would be the first thing on my list before I start dropping money on cams.

And since you like to run that weird rocket fuel in your car, I would suggest this route first.