Does it actually make a difference other than you increase watts when going up in gears?
increasing watts makes you go faster.
like IRL best find a gear your are comfortable riding in. For hills lower gears but on flat sections usually in your high gears.
everyone is a bit difference in cadence from between 70-100rpm is the normal range.
If you have two riders identical in every respect (bike, weight, profile etc), putting out exactly the same power, but one is slower cadence higher gear and the other is higher cadence lower gear. Would that make a difference to speed over any given course?
I think their speed would be the same.
The question is, which rider is more comfortable sustaining said power at said cadence and therefore can maintain said power longer or feel able to attack.
I think the same can apply to riders of different weight but then it’s W/kg at a given cadence.
Except if one rider is taller, his CDA would most likely be higher… therefore slower.
Its why roll out would matter.
Hypothetically…per min.
Rider A cadence 100 rollout for his gearing is 50” (5k)
Rider B cadence 104 rollout is 48” (4992)
Rider A pulls away unless river B lifts Cadence to 105…
Basically, I feel Zwift is really only about CDA and WKG….
**in the end, doesn’t really matter as it is a much more interesting way to get work in! 
You’re right.
I forgot about frontal area.