I mounted mine Dead Center with Griffons - but they were solely a park ski. They were AMAZING on rails and jumps at center, carving was pretty decent too. That's where I'd recommend putting them if they're going to spend most of their time in the park. If they're gonna be on the groomers a lot, then go with recommended (I think it was -2.5, but I can't remember exactly).
~WAKIN' UP THE NEIGHBORHOOD TONIGHT!~