@Bolthouse I use a 1280x1024 LCD in my cabinet and I think it works great. 4:3 would be 1280x960 with letterbox bands 32 pixels high on the top and bottom. You might try some of the libretro emulators to see how games look full-screen vs. 4:3. I like the barrel-curve shader with scanlines, so I want every pixel available. This would be 5:4, but I honestly, with the curvature I don't notice the difference.
Another consideration is this: If you will be playing any vertical games on the screen mounted horizontally, you might want to take advantage of all of the pixels you can--something that a physical bezel would prevent. You'd be limited to 720x960, when you could get 768x1024. Just a thought.