If you're rendering far less pixels than what's visible on screen you're not taking full advantage of the clarity your HMD can offer. However, that doesn't mean that there aren't benefits to a higher resolution screen, namely the screen door effect
The things that matter for GPU requirements are the frame rate of the HMD and FOV. Having a low-FPS mode can make demanding games like easier to run. High FOV is more demanding because you need to render more pixels for a given clarity (2/2)