What Ross said. From what I've read here, European standard for mechanical mitrals goes up to 4.0. Mechanical mitrals (I've got one) call for a relatively high INR.
Didn't quite understand your insurance statement. Your insurance will only pay for brand-name Coumadin, not for generic Warfarin? If so, no great loss - I'm on generic Warfarin because of the added expense of the brand-name drug, and I've found that my INR is more stable with the brand-name stuff. Apparantly it's common for the brand-name to produce more stable INR's than the generic.