First performance tests with CRT-GEOM Deluxe are very promising - I see significant performance increases on my machine (performance numbers in brackets are from these tests here) with old games. Interestingly newer games seem to loose performance, but still perform in a very healthy area:
1942 (Revision B)
BGFX/Metal-CRT-GEOM-Glow, Window - 650,30% (vs 212,08%)
Defender (Red Label)
BGFX/Metal-CRT-GEOM-Deluxe, Window - 501,07% (vs 742,88%)
BGFX/Metal-CRT-GEOM-Glow, Window - 449,59% (vs 200,70%)
BGFX/Metal-CRT-GEOM-Glow, Window - 336,37% (vs 191,21%)
Out Run (sitdown/upright, Rev A)
BGFX/Metal-CRT-GEOM-Glow, Window - 398,24% (vs 627,28%)
BGFX/Metal-CRT-GEOM-Glow, Window - 472,44% (vs 633,44%)
Configuration: MAME 0.176, QMC2 0.66, Throttle Off, run 60 seconds, for details, please see this post.
In the BGFX section of QMC2, you can now directly insert crt-geom deluxe for the chain, and you are ready to go.
I applied changes to the .json file as described here for GLSL in the same way. More details will follow.
Conclusion: BGFX in MAME gets better and better, and it also seems that the shader is gaining performance. So for everybody that had performance problems before, MAME 0.176 is definitely worth another try.