There's a working solution here: http://www.wsgf.org/dr/sin/en
It's vert- but still better than stretched imho. Should work with both the GOG version and the Steam version.
For me personally, I prefer to maintain the original aspect ratio as opposed to running widescreen with vert-. I hate not being able to see as much as was originally intended. If a hor+ widescreen option is possible, though, then I'd always try to go with that, but never vert-.
Just tried the fix out again, and it actually seems to be Hor+ if you use the fov command after applying the patch.
Even the screenshots on the fix page show it's Hor+, so I'm guessing the Vert- mentioned on the fix page might be a typo.