For better image quality, please adjust the resolution that you run games with. Official suggestions are: 1280×1024, 1600×1200 or 1920×1440 based on game performance.
1920×1400 would result in image quality like native apps. BUT: for a fluid VR experience, you need to make sure that games run at 45fps. That should your primary concern when adjusting resolution and detail settings.
Not sure about your performance problem. In Geometry 3D mode you may see a performance drop of up to 66% compared to playing the same game on your monitor since everything has to be rendered twice and some additional overhead. You can enhance performance by lowering a game’s resolution and/or detail settings or switching to Z-Buffer 3D if a game supports both 3D modes. Z3D doesn’t look as good, but is a lot faster.