My setup is working great with d3d9ex, portaudio etc so I had a play with frame delay to try to reduce lag further.
i5-3470, HD5450, super resolutions, GM 0.205. The test game was Shinobi.
50% of the time I launch the game, I can run up to frame delay 6 before I start getting slowdown and audio stutter (no tearing though).
The remaining 50% of the time, even at frame_delay 1 I get tearing about 1/3 down the screen.
The tear/no-tear state seems to persist within each instance of MAME.
Any ideas? I wondered if the 5450 is struggling to blit the 2560 wide mode, but that doesn't explain why sometimes it works up to frame_delay 6 without tearing?