You should read my posts and not some trolls intentional misrepresentation of my posts.
I wrote, very clearly, that Semnoz and Alp d'Huez were better examples of questionable performances. Riders said there was a tailwind, the video shows a tailwind. Many of the experts, like Ross Tucker, who calculate W/kg and VAM for most stages agree there was a tailwind. Pointing this fact out is not a declaration of support for Froome, just that there are better climbs to use as a measurement.
I doubt a clean rider will ever match Pantani on Alp d'Huez, Hautacam, etc. What is the limit? Don't know, 6.2 w/kg for 30 min or over is certainly questionable. 6.4 w/kg should set off alarms...6.7, Pas Normal. That is Riis, Pantani area.
Here is an interesting link to some of the best outputs of all time, and some from this year.
http://tour-manager.freehostia.com/start.php