.. as a rule of thumb .. edit: uphill 1.5min below 25km/h [15mls/h] the lighter bike [frame/wheels] has an repeatable time measurable [in seconds] advantage against an appropriate aero bike [frame/wheels] with the same rider [in different shapes] in the same group [in the same shape] ..

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___/\___/\___/\___ the s u r f b o a r d of the K u r p f a l z is the r o a d b i k e .. oSo >>

I'm sure with a calculator such as cyclingpowerlab you could determine the point at which weight becomes more important than CdA. But from my analysis, even for a course with a net uphill, an aero bike can still be an advantage, more so on a course with descending and flat sections.

Because of observed performance differences, or because of feel differences?

And if feel, how much of the difference is actually due to weight, or to fit and geometry and ride characteristics?

My '83 Miyata weighs about five pounds more than my Emonda, but the two bikes share very similar feel and liveliness. (And similarly, if I lightened my Campeur so that it weighed the same as my Miyata, it would still feel and pedal like a truck.)

I spent some time playing with a watts calculator one time and it really helped me to put things in perspective. For a person puttiing out about 150-200 watts, one pound of weight added adds about 1 watt required to maintain the same speed up a hill. When you make it a rolling course, that watt pretty much disappears.
Research Tom A.s articles/computations about to debunk any myths about weight. You could gain more speed upgrading from a GP5000 from a 4000 than you could trying to pare 4 pounds off your bike. If I was to make a hierarchy of importances it would go something like this:
1. Aero
2. aero
3. aero
...
8. aero
9. Rolling resistence of your tires
10. weight of your bike for hill climbs

31. weight of your bike for everyything else.
...
100. Rotational weight of your wheels.

The bike industry as no intererst in telling people weight does not matter much. I once tested a 10-pound difference (I filled a water bottle with sand and a seat pack with heavy tools) over my tt test course and came up with no discernable difference. For 10 pounds!
People who love the "feel" of light will argue all day and the only way you could shut them up is to put a power meter on their bike and show them the truth.