image quality

As a general rule of thumb yes- it's a noticeable difference. In my experience it becomes particularly noticeable when jumping to 6k+, since that resolution is also often tied to updated/upgraded rigs among many studios using more recent cameras. Same can be said (again, just generally) about the jump from 4k to 5k.

That being said there are plenty of studios who currently shoot in 5k and whose scenes look absolutely great even when compared to "higher resolution" scenes from other studios (SexBabes comes to mind). Older SLRO's are another example of 5k scenes that hold up very well.

Lot of factors make up the visual quality beyond raw dimensions & pixel count.

Lots of scenes have "fake" 6k or 7k.
The difference from a 4k or 5k scene to a real 8k scene is huge.

albertleder Yep, sadly that's very true. You can shoot a scene in 5k and render it out at 12k, but doesn't mean it'll look any better.

sheldoncooper
Mostly yes, I would say 5k is the minimum where scenes can be considered looking good, 4k is watchable, everything below basically unwatchable.

But the number of pixels is just one thing that determines quality, there are many other factors, especially the lens and also the post processing, and you can make a video that looks terrible in 5k+ too.

But generally I would say the jump from 4k to 5k+ is the biggest jump ever, most likely also to other factors then pure resolutions. Up to 4k many scenes where basically shot with something similar to GoPros or sometimes actually GoProsl But these are no better than a phone camera with a fisheye lens in front of it. With the transition to 5k+ there usually also was a transition to more serious cameras.
While 5k is nowhere near to be called enough, the 4k to 5k+ transition was probably the biggest we have ever seen and will stay that forever at least for porn.

In VR autofocus would be quite distracting (and actually is often even not possible with current lenses), and actually you do not even know at the time of shooting, because ultimately the viewer decides what to focus on. So the goto thing would be shooting with hyperfocal distance. But larger and therefore higher quality sensors, larger and therefore more light sensitive apertures and higher resolutions all reduce effectively DOF, and therefore hyperfocal distance gets farther away from the camera, too far for typical porn distances. So you have to find some compromise, to still get the front decently in focus, while at the same time keeping the background decently sharp.

It can already be seen in todays 7k and 8k videos that outside the sweet spot render resolutions is not the limit anymore, but the optics are. So while for something like landscape VR-Videos higher resolutions would still provide a huge benefit, for porn this would be a lot lower.

It probably goes without saying, but a huge amount of it comes down to how a scene is initially shot and the post-production + rendering used. A properly-lit 4k scene with some well managed post-production balancing & proper rendering can look a hell of a lot better than a poorly-shot 6k+ scene on a "superior" camera.

ableman

interestingly a lot of Japanese vr is 4k60, but it looks like it’s properly sharpened so the well done ones look pretty good while being smaller and having better performance.

Resolution is not everything, also basically no camera has a true "native" resolution, basically all the cameras only really capture one color for each pixel, and have to interpolate the missing ones. So technically, it is impossible to be pixelperfect in for basically any camera that is available. This also means a video rendered in 4k should be better when coming from a more modern 5k+ source then from a "native" 4k camera.