I would steambox that so hard 😀

I would, but no Firewire or capability for having an x1 firewire card using 2 GPUs...

Put the 2nd GPU in the bottom 8x slot and use the middle 16x slot for your add-in card. The PCIe 3.0 8x slot won't be bottleneck for any GPUs. You'll need a case with 5 PCI slots if you're using double-slot cards though. What are you still using that needs Firewire?

I've got a big case currently, so that actually might work. Firewire is for soundcard (Saffire Pro 40).

what u using firewire for? audio interface? i know some still using firewire... but it already on end-of-life / replaced by usb3/thunderbolt basically all asus ws board is great board imo (stability/reliability wise) although availability sometimes kinda low

As above. All the new ones are USB/TB now, but FW ones are still available (and cheaper). I would go for the full size WS board but that thing is overkill for my needs, still rocking the X58 version with a 6 core at 4 GHz, rock solid for 4 years now.