Beamrace mode unstable on my crt

[vagrant]

I'm having some stability issues with beamrace modes on my CRT running 720x576@50.
The test bars are very jittery on most slice settings (even 1), 10 slices is noticeably less jittery for some reason, but still far from stable.
Vertical scrolling in general is smooth on a few slice settings, 1 & 10 for example.. however I get tearing on the majority.
I'm also getting audio stutter with beamrace enabled on all slice settings, even 1.. increasing audio buffer doesnt help. Disabling beamrace = no audio stutter.
Any ideas?

D3D9/11 exhibit same behavior.
GPU & CPU usage is quite low..
Display is from a Radeon R9 380X via VGA out.

[Octopus66]

I find beamrace stability varies on my machine depending on screen resolution and gfx card. I find using onboard Intel gfx @ 1280x720 HDMI 50Hz with 2 slice provides the most stability, and other resolutions and cards have varying degrees of jitter without any clear pattern I can detect.

[vagrant]

I tried a bunch of other resolutions including the monitors default, but other then the tear-lines moving higher/lower, the results were much the same.
Perhaps beamrace is more suited for 16:9 displays and does not like my 4:3 modes?

As for the sound, the only way I can get it stable (using wasapi) is by disabling vsync modes entirely.
I did notice there were more sound issues using 020 CE mode vs. a500 CE.. but cpu usage is low in both cases.

[Mclane]

I tried beam race on James Pond 1 and the more slices the more screen breakup in the background. It's a 16:9 monitor but set to a 4:3 res.