I believe the reason all the companies have the disclaimer is due to the internet inflated amp draw the Mark VIII fan has been accused of.Every PWM controller description on their site states it, as does a few other controllers they offer.
"This controller Will Not Work using the following 2-speed O.E. Electric Fans: Dodge Viper, Ford Taurus, Ford Contour, or Lincoln Mark VIII. These fans exceed the amperage & functionality capabilities of this fan controller. "
What is strange though is the same statement can be found even on their high amperage dual fan controller. If the controller can't even handle Contour fans then I don't see how it is "High Amperage"
I think you are correct, the Mark VIII fan pulls higher amps.
There is a website for some dude that sells multiple relay controllers, and he has actual numbers of the steady state draw as well as inrush for the Mark VIII. I'll see if I can scrounge it up.