One other thing you will want to check is the shader complexity used for your particle materials (press F5 in game). Make sure that you’re hitting your target framerate! From experience, oculus rift handles lower frame rates better because they have time warp which gracefully handles any judder. The Vive on the other hand, NEEDS to hit 90fps because that is the hardware refresh rate, and anything less than that causes noticeable judder. If you’re making a game to support both HMD’s, develop for the stricter rule set constraints. Generally speaking, VR can start getting a lot of performance problems when you use a lot of transparency (caused by overdraw), but that doesn’t mean you can’t use it. You just have to be very smart and clever about optimizing things and “faking” it.
Also: I’ve never had any issues with the sky in VR. The skybox is generally far enough away that the lack of depth isn’t noticeable.