I've been there 3 times, most recently last Xmas.

In fact been there at around Xmas each time, and that has been perfect weather.

July/August is a zoo there I understand.

Train derails a lot from Cuzco. Last week all tourists on it were stranded for 2 days or whatever, and they needed to walk 20K or something.

They plan to double entry fee and half visitor numbers, so make it SOON I suggest.