Received.  Very much appreciated.

I have a 4 x 5830 setup similar to yours.  I can't keep the cards at an acceptable temp when all 4 are sandwiched that way.  I haven't yet tried to use spacers in the cards and I'm playing with side panel fans as well.  I've already turned the rig on it's side (even though the case isn't designed to rest on it's side) to keep the heat from affecting the other cards.

Your only solution may be extenders.

Also, you may want to check out the shrouds around the cards.  On some cards they're decretive and on other cards they force air over the cooling fins.  If they're decretive, you should take them off, as it will improve air flow between the cards.