Mash / Cinelli Vigorelli

Also, not everyone uses the same stem length/bar width, that can make the 58 a-ok or unrideable for people with the same height.

Some of the advances in stiffness (with the materials used or with different approaches to achieve common 'technologies' like tapered head tubes or double crown forks in DH), mostly boil down to the rider feeling more confident in what they are riding and that can make a difference when they are riding. If, in a blinded test, most of us can tell the differences is another matter, but the mental aspect does play a part in it.

Something like 6 or 7 years ago I remember reading a horror story with a carbon bar snapping and the rider getting quite disfigured from going down (he was wearing a helmet, but not a full face helmet as it was 'only' his XC bike). Reading that, made me quite afraid of carbon in general even though I know that today it doesn't really make sense with companies like Enve and all the advances made in carbon used specifically in bicycle applications. Something made of aluminium will fatigue eventually and snap, I'm also aware of that. But, that mental side of things makes me uneasy around carbon.

The tapered head tube, for me, ends up being that. If I can have one without it and one with it, I'll go to the one with it. I don't have reason to believe that the one without it will fail catastrophically or that the one with it won't fail at all. But it does give me a bit more peace of mind, without being a deal maker or breaker.

tapered headtube is big in dh, and no wonders why it has been popular.

but we are talking about a street frame, with a 'front brake friendly' interface, of sizing that is being aimed clearly at kids - really can't see anything 1 1/8 not being strong enough.