well i don´t know about others, but i´m not having problems with that.
Both my cards are running at full speed and nothing ever crashes.
Only problem I have is that i can´t oc my amd card while it´s not the main display adapter.
But i can simply plug in my monitor in the amd and oc.
I fixed this by applying my oc in the graphics bios.
Oc-ing nvidia cards is not affected by that.
same here, have to plug a monitor... (however, I think I loose only the control of the fan, if I unplug it... need to check that again...)
By the way is it safe to use a riser ? I tried to put today the 780 on a riser, and it seems the performance was affected and I also had a crash...
I think I will buy a new motherboard... I am still on a microatx...

The cards will have more space to breath...