GPU Extender
I got 4 290x and this motherboard

I had an issue though where I couldn't install more than 2 cards without having the GPU fans stop working.

Do you know if GPU extenders are a good idea if the purpose is passwords cracking? and if so what do you guys recommend?

If you mean risers, they work fine.
I only tested the USB3 based ones though

I don't really know what they called, but from the pics I saw they look the same to me.

I'm thinking of something that allows a GPU to set outside of the motherboard (and case).

Is there any risers that you recommend?
these seem to be pretty reliable:
That's what i use more or less. I can't tell the difference with a card in the box and a card outside, except the temperature Smile