Three-month followup: I decided to replace my Pedro mount with the upgraded (987) mount. The extra vibration transmitted to the cabin wasn't bad, but the effect it had throughout the cabin wasn't tolerable for long-term use. Anything that could rattle did rattle (the lenses in the map light, parts of the convertible top when it was up, the center console, etc.).
This is of course not a criticism of Pedro's product - as he's stated repeatedly, the racing mount DOES transmit more vibration to the chassis. At the track, it does a great job of anchoring the motor to the chassis. On the highway at 3,250 RPM, it does an equally stellar job... but you may find as I did that you didn't want a solid mount as bad as you thought you did.
If I blow through the 987 mount too quickly, I'll probably try a Pedro enthusiast mount, but the racing mount was a little too hardcore for me. I should have heeded Pedro's advice on his site.
All that said, it's still a great product. Thanks, Pedro!