I have done instrumented flow test on both using good scientific methodology to get good comparison in a controlled environment. The data is here:
The bottom line is that the duckbill eliminator has as low flow resistance as the best rubber style duckbill, but not as good as a silicone duckbill. The silicone duckbill has extremely low flow resistance. But when the flow resistance get so low, does it really matter...
Lets just say that I have no plans on ever again buying a duckbill. The convenience of the duckbill eliminator is so superior that I have no intention on ever using a duckbill (with only one exception, just to keep one regulator original).
Now I really only dive a Argonaut Kraken, which has the lower flow resistance of any double hose, all my other regulators that I used to dive have duckbill eliminators.