I forgot, I turn the SLI only for the card temp. Well, I realice that in "Split frame rendering mode", not only one card is working, and the temperature is slighty lower. Its goes this way: no-SLI: 72C - 57C. SLI on: 69C - 68C.
Anyway, not sure if this trick is really very useful. Perhaps to have a long-live video cards (that of course you´re going to change next year, hahahaha).