I would like to mount the GPU rotated 90º relative to the slot (with a raiser cable), custom secured to the chassis in a free area towards the front of the case.
The radiator would be immediately above the top end of the GPU. Somewhat like the right side of the image below.
Would this be ok? In terms of water circulation, keeping the GPU working and properly cooled?
I think you are meant to keep the GPU horizontal and have the Radiator hoses as close to the same level as the top of the card as possible.
This should minimize the stress on the watercooling pump as possible.