I've heard a few different opinions from various folks and experienced racers... No consensus. So I made some to try myself.
I made some Delrin mounts (upper and lower) last Sept and used them at Peterborough. I didn't like the change. I didn't notice much difference in handling and the vibration went up by a tone. The whole boat rattles. This is with basic mechanical tilt tube steering.
Thinking of changing just the upper mounts back to factory ones but they are buried under the engine block so I'm waiting for the right time to do it.