Hey, thanks so much for this.
I started fiddling with the A05 release a few weeks back, but quickly noticed the frequent horizontal switching on PSX was not great for my PVM, so I hacked about with the GPU code and got it outputting at 2560 wide which worked perfectly. I see you've included this feature in the newer version which is great.
Another issue I had however was with how Mednafen itself handles positioning/overscan, for example, at certain horizontal resolutions, you either end up with stuff being incorrectly cropped, or extra black bands being added (note how screenshots are never the right res). I eventually managed to get the code working so that the output was exactly perfect with no black bands or incorrect cropping, save for a slight crop at the 368 res which wound up at 365 (due to it being @ 2560).
Would you be interested in fixing this issue in your version? I can supply some diffs if you'd like to see what I did to get it working.
Cheers