Watch your heat with those duels. Though, I'm sure you already know that.
I will, those pistols get hot.
(Sorry, could help myself.)
Seriously though, they are fine. It will be even better with the Big Bang as I can remove the sound card that is currently between them. Allowing the top one to get a bit more air. (My other PCI-E 1x slot seems to be dead so I have no choice ATM but to use the one between the cards. It "blocks" half the fan on the top GPU though and it's always 1-3C higher than the lower one.)