Static stiffness aside, any mount designed for a engine that isn't a 3cyl or a 5cyl is going to be extremely harsh at idle. The large amplitude of the vibrations are greater than what the decoupler is designed for. The mount will immediately hit IOD. Even worse, at 750RPM those vibrations are going to be at 12.5hz. This is right around where most hydro-mounts are designed to have the highest dynamic stiffness in order to combat smooth road shake.

http://i.imgur.com/LjAcrJx.jpg