Is there anything supporting those cards upright from the table or is it just a single L bracket along the top of the card brackets? I'm just wondering if you are still letting them be supported vertically by the slot, or if you have something else.
Just the single L bracket along the top of the cards, with all the cards screwed to it it's very sturdy. I was having issues with the first card moving too much in the PCI-E slot, the others not so much, but GPU3/4 the screws in the rear of the cards were touching the fans of the card behind it till I put in some foam spacers as a temp fix. Now with the bracket its 1000x more stable.