Ok, so answer the 20 min effort vs 40+ minute effort question, I only have limited information from elite athletes, so this isn't a University study....
That said: CVV can produce about 5.9 watts per kg in peak form for 40+ minute climbs, Wiggo is a bit more at 6.1 w/kg for this length of effort.
From the pre-Tour tests both riders have done up Rocacorba (a 33 minute climb) I know that Wiggo was at 6.1w/kg and CVV was 5.7 w/kg (He was off form a bit in June). However, Wiggo did a local 10 mile TT in GB about 2 weeks before the Tour, or 5 days before the Rocacorba test. He posted a time of 18mins flat (and was disqualified for using a 1080 wheel...funny rules over there). Anyhow, his power was 482 watts, so using his Tour weight of 72 kgs, so 6.7 w/kg. So, anecdotally, there's about a 9% decrease in power when going from a 20 min effort to a 40+ min effort. At 6.7 w/kg you certainly can climb at a VAM of 1750, but at 6.1 you wont even hit 1700 (again, anecdotal based on experience).
The last TT in the Tour Wiggo averaged 434 watts, consistent with his previous tests of 40+ minutes and just about 6.1 w/kg. I dont have any data for Wiggo up climbs in the Tour, as he didnt use a PowerTap.