Whenever I try these VR setups at shows, there's noticeable lag in flipper response. Even the new ones being sold by vendors have this problem. Is it because these are using second-rate hardware? Is this still a problem with custom high-end systems? Has this been overcome on any platforms?

It'd be more interesting to know what the lag on the simulations are. The FPS analysis makes sense, and I'm guessing these are mostly running at 60fps, but I'm skeptical they are responding by the next frame. If it were, that would be ~17ms. Likely it's 2 or more frames, which puts it in 30+ ms range. An order of magnitude slower than the real thing, which is why it's so noticeable.

Has anyone built something that gets 144fps? I guess you need substantially more expensive monitors then, which the pre-made commercial ones likely don't use. I suspect there's more in the software simulation that prevents next-frame response, and even on those high-end systems, the 7ms theoretical reaction isn't actually achieved. But would love to hear subjective opinion if anyone has such a setup.