Welcome to Subsim diamondthree.
Your questions are a bit outside of my tech-knowhow. However, Rubini did a lot of work relating to the creation of a widescreen environment for SH3... (Which does not offer a selectable widescreen resolution option as you have found.) ...so just to get you started on the path tonight, you may research his posting history here to get closer to the answers you seek.
Otherwise, just let this thread cook for a day or so and someone with a bit more experience dealing with resolution issues will be along to help without a doubt.