Once the sting in your wallet fades I’m pretty sure you won’t regret the 3090. I think for this game you really do need more vram than the 3080 if you want to run at the higher resolutions the quest supports.
I think the 3090 has a bit more overclocking headroom too if you are trying to wring out every last fps.
Plus if you play any other games you’ll be in heaven. I play onward and can supersample up to crazy resolutions and still hit 90fps.