From Mihai Simions blog
Zoncolan 2007:9,8 km@12,2%---39:03---average speed 15.06 km/h(Simoni-Piepoli)-RECORD
Mortirolo 1999:11,7 km km@11,1%---41:42---average speed 16.83 km/h(Gotti-Heras-Simoni)-RECORD
Angliru 2000:12,8 km@9,6%---41:55---average speed 18.32 km/h(Roberto Heras)-RECORD
Finestre 2011:18,3 km@9,2%---1:02:09---average speed 17.67 km/h(Jose Rujano)-RECORD
Finestre is the hardest.
Rettenbachferner is also harder than Zonc, Mortirolo and El Angliru.