Hi Allottho,
did you find some other solution ? I am also trying to do panorama viewer with quality like Samsung VR app with 8k images but all looks terrible. I tried 4.19 with vr.pixel density set to 1.419 and it looks I think better but material for viewing stereo images not working. Need to wait for final release.
Are you using sphere with material setup like in this tutorial for viewing streo images?