Some videos to help your search (but at 45 kph, so not quite the same).
Summary at 5:59
Summary at 9:03
Summary at 9:00
IIRC, the one test is only aero bikes, while the others have some regular ones. There's definitely a > 20 watt difference at 45 kph. The difference between the fastest and slowest in the aero position across all three tests is almost 40 watts. There are likely other variables affecting this (they were in different tests) but I suspect the difference between a good aero bike and a regular one is going to be at least 10-15 watts at 20 mph.