Most contact mic recordings I've made (or heard) have very little information, if any, going on at 18kHz. Attached to many materials like metal, wood, or glass, you'd be lucky to get a ton of information above 5kHz in a recording.
If you are looking at doing some extreme pitch shifting, you are better off using a high-frequency response condenser mic, or a contact mic along side a condenser mic. Of course, contact mics by there very nature, can make objects sound larger without any pitch shifting.
If you're going to record a golf club hitting a ball. I'd suggesting mounting the mic not on the head, but further down the shaft of the club. It will give the vibrations in the club further distance to travel...making for a more interesting recording.
Some other options to consider:
- Barcus Berry Planar Wave
- Trance Audio Inducer
- Cold Gold
- Building Your Own piezo (it's not that difficult if you're handy with electronics)