I'm curious -- which hardware devices? I find Vive and (current-gen) Oculus Rift the most comfortable. The biggest issue for me playing a well-designed game is fogging up due to sweating.
EDIT> I have a relatively low tolerance for motion sickness.
EDIT> I have a relatively low tolerance for motion sickness.
I've read that this is a problem for astronauts IRL when they're in free-fall next to a slowly rotating or panning object that occupies a lot of their field of view. So, that would be a kind of existence proof that it's not vergence, but rather optical flow that is decoupled from the subject's actual motion.
It sucks, but basically FPS games are out for VR, until you can actually run around, leap, etc.
EDIT> Another example -- during a scene in Apollo 11 where the camera (and hence my view) was orbiting the spaceraft while my IRL body was still, I started to feel queasy. I was able to reduce the sensation by looking at the growing space-craft as it started to fill more and more of my field of view -- it was relatively stationary to me. This again speaks to optical flow, and motion that is out of whack with what the player's ears are telling them. Another cheat along these lines is to use a cockpit that is fixed relative to the player's view to reduce the amount of visual area that is giving wrong motion cues.
EDIT2> I'd be interested to know whether you can last longer in a game that uses only your own IRL motion + instant teleport. So, no thumbsticks, mouse, keyboard locomotion -- as these are all known chunder inducers. Unfortunately non-VR games with bolt-on VR are like the worst-case for comfort, but also often the games that we really want to see in VR.