Very few riders would be able to match your "ceteris paribus" condition, as people ride bikes with somewhat similar, but never really identical geometry, outside of trail/flop.
Besides, what is the definition of "substantial"?

During the last year or so, I mostly rode 2 bikes with very closely matched geometry and weight distribution (light front bags on mini-rack), which differ mainly in trail - the A bike has about 64 mm , and the B bike has about 39 mm of trail.
Same roads and mileage. Speaking strictly about downhills, inducing lean (or change in lean) for the A bike takes just a thought, with a very subtle push on the handlebar, while the handlebar of the B bike demands a more pronounced input for the same amounts of lean/lean change.
The downhills I do are all in a tucked mode, hands in the drops, speeds vary between 30 and 65 mph. I have been riding for 52 years and still fail to understand why would someone ride downhill on a dry paved road on the hoods, or with low speed, or with a very firm grip...

It seems to me you need to work on your body and hand position for quite a bit, while riding a bike with a familiar to you geometry, until you learn that your weight is to be borne by your legs, that drops are good, heavy grip is detrimental, and speed is a friend. Then perhaps you would consider low trail.
I appreciate the low trail on a (lightly) front-loaded bike only on the ascends. The rest of the time it is of no benefit. However, where I ride (Appalachia), I am doomed to spend lots of time ascending, hence my low-trail bike....