Lian Li O11 XL and RTX 3090 air-cooled?

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As per title, helping my brother put together a PC.
For me, a custom loop is the way to go, silence and performance.
He loves the O11 XL, like mine, but don't want to go custom loop.
For those running their RTX 3090 on air, how bad should I expect the temperatures to be?
Plan is: Dark Rock Pro 4, which I can endorse, and populate all available places with beQuiet fans.
Vertical mounting would be any help?

 

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Thank you for the quick and helpful response.
I'm running a custom loop, on my "signature" system.
One thing that really stopped me running the GPU on AIR was the initial full-blast. Setting a fan curve was efficient temperature-wise, but a RTX 2080 doesn't generate as much heat as I'm expecting the RTX 3090 to do.
If worth mentioning, he is getting the Zotac one, I know, but was the only one he could get now. As he doesn't OC his gear, I doubt the power limit would be an issue.