If you use one of these, you don't have to use extenders (4 cards fit fine on these boards). I use them for the convenience.
MSI 790FD-GD70 ($)
MSI 890FD-GD70 ($$)
Sapphire Pure Black H67 ($$$)
MSI Big Bang Marshall ($$$$)
It cost more but more importantly, you have to fight heat as there's less than 1cm between the cards.
@kripz: I dig that, I think I'll convert all my cases to it... Question though, how do you clamp the boards onto the shoe rack?
you dont. They just sit there, the pci connection drops through the grate. If you're worried, cable ties. again, $2.