I feel like 3d is much less demanding than vr since your view is fixed to the movement/look sticks?
I think the way you rotate the view (using VR headset movements or your mouse/controller/gamepad) doesn’t have a significant impact on performance.
If you don’t care about Full VR mode, you can play with Immersive Screen Mode and disable headtracking if you want (or even Cinema Mode) but it’s not the most important thing.
But it’s true you’ll need a lower resolution if you don’t zoom in as much (reduce zoom / scale).
And so “Full VR” mode usually recquires more resolution to get a perfect image quality (unless you configure a really huge screen around you with Immersive Screen, which can also benefits from high resolution in this case).
Theoritically, pure 3D (without a VR headset) could be less demanding than VR but it’s not always true (it doesn’t seem to be the case at all with my 3D glasses-free monitor, compared to VorpX with the Reverb G2 at higher resolution and much more details).