I only have up to 310 watts maximum, normal gaming load is <300 watts.
The cable will be tight in the O11 if it's horizontal, but I recommend installing it vertically anyway.

For the size, you need to check with the dimensions of your case. This GPU is not at all efficient. It's very powerful and consumes a lot of power.

This gpu is big 360mm say also 370mm, I don't type fūr pc case as Lian-Li, but normally it already says in the technical detalien which gpu fits. Consume ūber rtx4080 are all the same, 425watts at 100% load. Otherwise it's always less, about 325-350watts netti.