Here's what I posted immediately after stage 11:
Interesting day, not decisive but telling. Here's how I see the GC chances:
Aru - 60%
I think pretty firmly that this guy's going to pick up his maiden GT. He was clearly the best today, and he's the only big contender without back-to-back GTs in the legs. He's middling in the TT, but he already has enough time on everyone but Dumoulin to possibly hold the lead even if it was as it is now. Of course, 3 more big MTFs before the TT mean that he'll get a half minute here and there on others before the TT if he continues to be the strongest.
Rodriguez - 15%
I can't believe that I think he has a chance at this, but he seems the most solid of the rest of the lot (except Dumoulin, but I'll get to him). He was pretty spent on the punchy finish the other day, and pretty spent at the end of today, so I have a hard time believing he can do more than just hang in there (although if he handles fatigue better than others, maybe he can claw back some time on the 3 MTFs). Basically he needs to stay solid and hope that either Aru's performance today was a fluke, or that Aru bonks and loses a ton on some stage. But as it stands right now, he might be able to hold Valv and Majka off in the TT with a minute on them. The others within 3 minutes (Nieve, Chaves, Moreno) are some of the few GC guys worse than him in a TT.
Dumoulin - 10%
He hung tough today, and that was impressive. Plus, guys will need at least 3-4 minutes on him in the TT. But I think they'll get it. Doing well on the punchy climbs was expected, if not to the degree of winning vs. Froome/Rodriguez. Doing this well in the high mountains is a surprise, but it's just a stage. A GT is a grind, and he's not used to that kind of recovery. I think it's pretty good odds that he bleeds a lot of time on at least one of the 3 MTFs, and probably all of them.
Majka - 5%
Not quite good enough to go with the best today, but held his own well and came back to within a handful of seconds to Purito. Could be a sneaky good pick going forwards, is okay at TT, is an attacking rider. I favour him for a podium, if not the win.
rest of the field - 10%
Who knows, we could be in for a surprise. But of all the guys that are close, Valv looks to be fading after a loooong season, I have the same doubts about Chaves' recovery as I do Dumoulin, and Nieve/Moreno are simply second-tier. If I had to pick a dark horse for a surprise, I'd pick Moreno, because he looked better than his leader today and doesn't have the Tour in his legs. But the hierarchy is clear at Katusha, so I think he's leashed (and seems to be happy working for Purito). Interestingly, Froome didn't pack it in today and is still in the top 15. Not that I think he could win, but he could pull a Nibali-in-the-Tour game of correcting himself and coming back up bit by bit.
After today... phew! Hard to read the tea-leaves in such a close stage, but I would maybe put Aru down 5% and put Quintana at 5-10% (with 'rest of the field' maybe going down to 5%). This could shake out in a number of interesting ways. First, with two steeper finishes to go in the next few days, it doesn't look good for Dumoulin that he lost a bit of time today, because one would think he'd stand to lose more on the next two stages. On the other hand, Purito looked strong(ish), and my prediction about him handling fatigue might come into play. Compare his ride on the stage Dumoulin won, where he waited and didn't make any moves, and then when he tried to come around Froome he just didn't have it. Then, stage 11, he's better than anyone but Aru (and Moreno) but has all the trouble he can find just following Moreno. Today, he closed on Aru after being gapped, put time into Valverde and Dumoulin, and briefly got away on some 9% stuff and was strong enough to hold everyone off by a second or a few. If he felt the same tomorrow and the next day on steeper stuff that's more his terrain (the 'gain 20-30 seconds in the last 1.5km' sort of climbs) then he's got a real shot. It's hard to get a real reference point given Aru's relatively short pro career, but I'd put him quite close to the (post-2012) Rodriguez in terms of flat TTs of this length... maybe I'd give him the edge because his skills are still developing, but it wouldn't surprise me to see these guys within 30 seconds of each other either way. If Purito is really close to Aru, or ahead of him, going into the TT, he could possibly have the lead after it.
On the other hand, the most interesting scenario would be if Dumoulin hung in enough to get the lead back by, say, a minute after the TT, with Aru and Purito on his heels. That would make the last few stages guaranteed to be pretty entertaining. I don't think it's going to happen, though. If he digs and holds on for dear life and is still within 90 seconds after these mountains, you've gotta think his tank will be pretty empty going into the TT and he wouldn't produce the normal performance one would expect.
But finally, I couldn't help but be struck by Quintana's performance today. If this is what he looks like the day after almost pulling out, I gotta believe he's got a (however long) shot at pulling back 3 minutes, especially if you think he's a better TTer than Aru or Purito, as I do. If he's indeed recovered from whatever it was and today is indicative of his 'real' level, it's a definite possibility that he could pull out a minute on the other guys in the next two days. I guess that still leaves a tall order to win, but I've got to give him at least a 5% shot.