man comparisons of the time ascents don't say much that often,only if you really did follow those races and watched all the factors involved.which is difficult.
as an example for me the most impressive performance on alpe d'huez is coppi's and by far. he did it in 45 minutes but watch out ,that was DA BOMB!!!he did it after 8 hours of racing!!!(stage of 260 km),on a pretty heavy bike and the roads back in those days were tough not like this.needless to say that le tour was something like 5000 km then.
that certainly is one of the most extraterrestrial performance i've ever heard of.people say that 90's blablabla epo blood transfusions blablala was the shiit but they are wrong.for me those guys riding in that era were out of this world.i don't even imagine those guys being one day in a grand tour awake,i think they were drunk or high every second because you couldn't endure pain staying awake like that,i don't think it's possible.
i've read also about bahamontes performances somewhere,puy de dome and superbagneres.out of this world.the pubers these days we'll say he was on epo,but even on epo you couldn't get close of those performances.