This is silly. Choose bottom gears you're comfortable with, not because they're fashionable.
If you want to be analytical about it, Protour Pros do 160km over big hills at about 40kph+ average on maybe 53/39 and 12-25 for 'average' stages. This probably includes keeping the 25 as a bailout cog. So if you riding similar terrain at 30kph average, one might scale gears accordingly which puts one into a bottom gear of 34*29. For mountains if pros are riding 36*28 up the Stelvio for instance, then a similar speed ratio (actually probably worse) suggests that normal people should have a slightly lower gear than 34x34.
My experience on Saturday confirms this - I rode up the Stelvio on 34x25 and needed to ride hard to keep the gear turning over, and the legs were wasted by the end, whereas people on MTBs looked much more comfortable. Well, apart from a guy in trainers who had a 6-year-old in a child seat. I gave him a push for a few metres, but not sure how far he managed
There was also a guy with a corncob cassette and Lightweights. He appeared to sprint one hairpin at a time, then take a break by the side of the road.
Regarding top gears, I think there's an argument to keep them similar to the pros, since 85kg desk jockies have a higher terminal velocity than 60kg Euskatel pros.