> You're still rendering each frame twice & you have the overhead of coding something > that is accurate to the original renderer by default (dither patterns etc) and can > also render in high resolution.
Yes, but you can render the frame twice much, much faster on the GPU. And if you want to guarantee pixel perfection, that's not a problem with GPGPU.
And you didn't put in any of that work in MAME's software renderer, as Javier Donoso likes to remind us.