I don't think there's any difference in proportional sizing. Why would a bike you spend 6 hours a day on be any different from another bike you spend 6 hour a day on? It's the same you, same issues with comfort and power production. The fact that one will usually go a bit slower on the flat when touring makes no difference. Headwinds exist on any bike. I'm 75, still ride the same geometry I've used on all my road bikes, or as close as that bike will allow me to get, which does vary, but I try for the same position. I don't happen to have a single tourer, rather my wife and I tour on our road tandem, same bike we use for sport riding, except that we take the captain's aero bars off so we can use a bar bag. I run a slammed -6° 90 mm stem on my long distance road bike and the tandem. The tandem does have a slightly taller head tube to allow for 3 tubes meeting there instead of 2. I don't notice much difference in fit.
If you're tall, I think an endurance bike geometry might work better than a full race bike with slammed stem.
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