Thanks for the super fast response.
I chose cubestrips over equirectangular images to minimize distortion around the nadir/zenith points.
Furthermore I like to just upload one image instead of 6 single images (custom backend built with strapi.io).
But you are right: cube faces outperform the other two, especially when dealing with larger images. AND since my split screen holds up to four panoramas next to each other (4 viewers), performance is key.
I now modified my backend to handle whatever type of image I have of those three mentioned. Would be still nice to have "onloadcomplete" working with cubestrips.
Cheers,
Hennes