900
@C : I gave it another try with an external 1920x1080 monitor this time.
Without surprise very limited possibilities. It would be preposterous to hope to combine heavy post processing with frame_delay and vsync_offset on that output resolution, using such a low end machine and see things go smoothly (i.e laptop i3-4030u, 820m)
Still, I could achieve tear-free (or almost) 1~3 frame_delay if using only classic options such as filter, prescale, and png effects, instead of HLSL.
Though even with such simplistic post-processing I had to push vsync_offset near 600 (or even a little more), which barely took care of the tearing, and anywhere beyond that level wouldn't help anymore apparently.
I think in a similar hardware+display configuration this 600 is the exteme ceiling, so much that the sane reaction to anyone with a similarly-performing PC should be "for 1080p get a better machine anyway"
And there I've tested only CPS and neogeo games which aren't too heavy systems.
For the 900p integrated display of before, vsync_offset up to ~590 was actually useful, allowing the use of HLSL with complete stabilization of f_delay 1~3
(more often 1 than 3 TBH)
So, maybe changing the slider limit to 600 or something would be a sound thing, maybe not, I don't know.
This is just complementary 'FYI' material, my purpose was to test lower end limits scenarios for flat panel users, somehow, though this is obviously no thorough benchmarking since it was done with only one low end PC, two displays, and a couple MAME drivers...
(this is pretty much the situation a non-negligible amount of users are in though, say, the casual/broke but who still wanna get a tatse of a little better emulation, so it's not unrealistic testing either)