In reply to GingerBread22:
I've done it a number of times in summer. I can't recall the exact dates. However, if you are planning on going via Valsorey I'd recommend that you did it as early in the season as possible. The section of the route up to the Plateau du Couloir is absolutely deadly in dry conditions, so much so that after one very near miss I decided it was just too dangerous and decided to completely miss out the Valsorey and started going direct to the Chanrion from Mauvoisin. As far as weather is concerned, personally I don't think it make a whole lot of difference whether you go July or August, though some think otherwise (in favour of July).