Do not use any external supersampling tweak with vorpX! vorpX already supersamples the final render textures internally, adding an additional external multiplier only leads to extremely large final textures without any gain in image quality.
Instead run the games at the highest possible 4:3/5:4 resolution that still gives decent performance on your PC for the game in question. 1920×1440 results in image quality comparable to native apps. Resolutions larger than that would result in supersampling, resolutions below that are upscaled before sending the image to the headset (but are usually faster, of course).