I have a similar setup with the Vapor-X's and my top card gets 79C at 1950RPM while the one underneath it gets 79C at 1200RPM. Anything over 2200RPM becomes extra noisy with these cards.
Listen to this man when you are picking out your motherboards people! Just because you have x pcie slots, does NOT mean that you are garunteed to be able to use them all at the same time. Sometimes as soon as you populate a 2nd one, only two of the three will work. Be sure to do your research and DO NOT assume! All will be well in your mining ventures if you carefully pick your components!!