Updated: Tubing routing suggestions (vote or come up with your own layout!)

[Waterlogged]

As for the tubing layout, I think I would probably go for #3, it seems to avoid the tightest bends and keeps the Supreme HF looking normal. I'd worry about the port/barb/tubing off the rear radiator that's closest to the motherboard tray, it might be too close to the board's VRM sinks and be blocked by that.

Actually, I'd be more concerned about the parallel GPU block setup not cooling either of the cards.